Supplemental Prospectus (Form 424B5)

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Filed Pursuant to Rule 424(b)(5)

Registration No. 333-277747

PROSPECTUS SUPPLEMENT
(To Prospectus dated May 20, 2024)

Mayville Engineering Company, Inc.

4,348,000 Shares

Common Stock

We are offering 4,348,000 shares of our common stock, no par value per share, as described in this prospectus supplement and the accompanying prospectus to institutional investors.

Our common stock is listed on The New York Stock Exchange under the symbol "MEC." The last reported sale price of our common stock on The New York Stock Exchange on May 18, 2026 was $24.92 per share.

Investing in our common stock involves a high degree of risk. Please read the "Risk Factors" beginning on page S-4 of this prospectus supplement, as well as in the accompanying prospectus and the documents incorporated by reference herein and therein, for a discussion of the factors you should carefully consider before deciding to purchase our common stock.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

We have granted the underwriters an option for a period of 30 days to purchase up to an additional 652,000 shares of common stock from us at the public offering price, less the underwriting discounts and commissions.

Delivery of the shares of common stock to investors is expected to be made on or about May 21, 2026, subject to customary closing conditions.

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TABLE OF CONTENTS

Prospectus Supplement

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Prospectus

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ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is this prospectus supplement, which describes the terms of this offering and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference herein or therein. The second part, the accompanying prospectus, including the documents incorporated by reference into the accompanying prospectus, provides more general information. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. To the extent there is a conflict between the information contained in this prospectus supplement and the information contained in the accompanying prospectus or any document incorporated by reference herein or therein filed prior to the date of this prospectus supplement, you should rely on the information in this prospectus supplement; provided that if any statement in one of these documents is inconsistent with a statement in another document having a later date-for example, a document incorporated by reference in this prospectus supplement or in the accompanying prospectus-the statement in the document having the later date modifies or supersedes the earlier statement.

We have not, and the underwriters have not, authorized anyone to provide you with information different from, or in addition to, that contained or incorporated by reference in this prospectus supplement, the accompanying prospectus or any free writing prospectus prepared by or on behalf of us or to which we may have referred you in connection with this offering. We and the underwriters take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. The information in this prospectus supplement and the accompanying prospectus is accurate only as of its date, regardless of the time of delivery of this prospectus supplement and accompanying prospectus or of any sale of shares of our common stock. Our business, financial condition, results of operations and prospects may have changed materially since such date.

This prospectus supplement does not contain all of the information that is important to you. You should also read and consider the information in the documents to which we have referred you in the sections entitled "Where You Can Find More Information" and "Incorporation of Certain Information by Reference" in this prospectus supplement.

We are offering to sell, and seeking offers to buy, and the underwriters are soliciting offers to buy, these securities only in jurisdictions where offers and sales are permitted. The distribution of this prospectus supplement and the accompanying prospectus and the offering of the securities in certain jurisdictions may be restricted by law. For investors outside of the United States: neither we nor the underwriters have done anything that would permit this offering or possession or distribution of this prospectus supplement and accompanying prospectus in any jurisdiction where action for that purpose is required, other than in the United States. You are required to inform yourselves about and to observe any restrictions relating to this offering and the distribution of this prospectus supplement and the accompanying prospectus. This prospectus supplement and the accompanying prospectus do not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by this prospectus supplement and the accompanying prospectus by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

Unless the context otherwise indicates, references in this prospectus supplement to "we," "our," "us," the "Company," and "MEC" refer, collectively, to Mayville Engineering Company, Inc., a Wisconsin corporation, and its consolidated subsidiaries.

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FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein, contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, Section 27A of the Securities Act of 1993 and Section 21E of the Securities Exchange Act of 1934, as amended (the "Exchange Act").

All statements, other than statements of historical fact, included or incorporated by reference in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein, including, without limitation, estimates, projections, outlook, guidance, statements relating to our business plans, strategy, objectives, expected operating results and future financial position, and the assumptions upon which those statements are based, are forward-looking statements. These forward-looking statements generally are identified by the words "believe," "project," "expect," "anticipate," "estimate," "forecast," "outlook," "intend," "strategy," "plan," "may," "should," "will," "would," "will be," "will continue," "will likely result" or the negative thereof or variations thereon or similar terminology generally intended to identify forward-looking statements. These forward-looking statements are based solely on our current beliefs and are not guarantees of future performance. Therefore, these forward-looking statements are subject to inherent risks, uncertainties, assumptions and other factors that could cause actual results to differ materially from those expressed or implied by such forward-looking statements, including but not limited to:

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We caution you that no forward-looking statement is a guarantee of future performance, and you should not place undue reliance on these forward-looking statements which reflect our views only as of the date of this prospectus supplement. We assume no obligation, and disclaim any duty, to update or revise publicly any forward-looking statements, whether written or oral, and whether as a result of new information, future events or otherwise, except to the extent required by law.

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RISK FACTORS

An investment in our common stock involves a high degree of risk. You should carefully consider the risks and uncertainties described below, as well as those set forth under the heading "Risk Factors" in our most recent Annual Report on Form 10-K, which are incorporated by reference in this prospectus supplement. Our business, financial condition or results of operations could be materially and adversely affected by any of these risks and uncertainties. In that case, the trading price of our common stock could decline and you might lose all or part of your investment. In addition, the risks and uncertainties discussed below are not the only ones we face. Our business, financial condition or results of operations could also be harmed by risks and uncertainties not currently known to us or that we currently do not believe are material, and these risks and uncertainties could result in a loss of all or part of your investment. In assessing the risks and uncertainties described below, you should also refer to the other information contained in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein, including our consolidated financial statements and the related notes thereto, before making a decision to invest in our common stock.

Risks Related to This Offering

Fluctuations in the price of our common stock, including as a result of actual or anticipated sales of shares by us and/or our directors, officers or shareholders, may make our common stock more difficult to resell.

The market price and trading volume of our common stock have been, and may continue to be, subject to significant fluctuations due not only to general stock market conditions, but also to changes in sentiment in the market regarding the industry in which we operate, our operations, business prospects or liquidity, or this offering. In addition to the risk factors discussed in our periodic reports and in this prospectus supplement, the price and volume volatility of our common stock may be affected by actual or anticipated sales of common stock by us and/or our directors, officers or shareholders, whether in the market, in connection with business acquisitions, in this offering or in subsequent public offerings. Stock markets in general have at times experienced extreme volatility unrelated to the operating performance of particular companies. These broad market fluctuations may adversely affect the trading price of our common stock, regardless of our operating results.

As a result, these fluctuations in the market price and trading volume of our common stock may make it difficult to predict the market price of our common stock in the future, cause the value of your investment to decline and make it more difficult to resell our common stock.

We will have broad discretion in the use of the net proceeds to us from this offering and may invest or spend the proceeds in ways with which you do not agree and in ways that may not increase the value of your investment.

We will have broad discretion in the application of the net proceeds to us from this offering, and you will be relying on the judgment of our management regarding the application of these proceeds. You may not agree with our decisions, and our management may not apply the net proceeds to us from this offering in ways that ultimately increase the value of your investment. We expect to use the net proceeds to us from this offering in the manner described in the "Use of Proceeds" section of this prospectus supplement. Our failure to apply these net proceeds effectively could result in financial losses that could have a material adverse effect on our business or cause the price of our common stock to decline.

Future sales or issuances of our common stock in the public markets, or the perception of such sales, could depress the trading price of our common stock.

The sale of a substantial number of shares of our common stock or other securities convertible into or exchangeable for our common stock in the public markets, or the perception that such sales could occur, could depress the market price of our common stock and impair our ability to raise capital through the sale of additional equity securities. We may sell large quantities of our common stock at any time pursuant to this prospectus or in one or more separate offerings. We cannot predict the effect that future sales of common stock or other equity-related securities would have on the market price of our common stock.

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USE OF PROCEEDS

We estimate that we will receive net proceeds to us of $81.6 million from the sale of the shares of common stock offered by us in this offering (or approximately $93.9 million if the underwriters' option to purchase additional shares of our common stock is exercised in full), after deducting the underwriting discounts and commissions and estimated offering expenses payable by us.

We intend to use the net proceeds to us from this offering primarily for reducing amounts outstanding under our senior secured revolving credit facility, capital expenditures focused on our relevant growth sectors and working capital and general corporate purposes. A portion of the amounts expected to be repaid under our senior secured revolving credit facility are attributable to amounts borrowed to complete the Accu-fab acquisition, which we completed in July 2025. Our senior secured revolving credit facility matures on June 28, 2028 and, as of March 31, 2026, the interest rate of such facility was 6.42%.

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MATERIAL UNITED STATES FEDERAL INCOME TAX CONSEQUENCES FOR NON-U.S. HOLDERS OF COMMON STOCK

The following is a general discussion of the material U.S. federal income tax consequences applicable to non-U.S. holders (as defined herein) with respect to the purchase, ownership and disposition of shares of our common stock issued or acquired pursuant to this offering. This summary does not purport to be a complete analysis of all potential tax considerations related thereto. All prospective non-U.S. holders of our common stock should consult their tax advisors with respect to the U.S. federal, state, local and non-U.S. tax consequences of the purchase, ownership and disposition of our common stock.

For the purposes of this discussion, a "non-U.S. holder" means a beneficial owner of our common stock that is not, for U.S. federal income tax purposes, a partnership (or an entity or arrangement treated as a partnership) or is any of the following:

This discussion is based on current provisions of the U.S. Internal Revenue Code of 1986, as amended, or the Code, existing U.S. Treasury Regulations promulgated thereunder, published administrative pronouncements and rulings of the U.S. Internal Revenue Service, or the IRS, and judicial decisions, all as in effect as of the date of this prospectus supplement. These authorities are subject to change and to differing interpretation, possibly with retroactive effect. Any change or differing interpretation could alter the tax consequences to non-U.S. holders described in this prospectus supplement.

This discussion is limited to non-U.S. holders that hold shares of our common stock as a "capital asset" within the meaning of Section 1221 of the Code (generally, property held for investment),. This discussion does not address all aspects of U.S. federal income taxation that may be relevant to a particular non-U.S. holder in light of that non-U.S. holder's individual circumstances, nor does it address any alternative minimum tax, Medicare contribution tax on investment income, estate or gift tax consequences, or any aspects of U.S. state, local or non-U.S. taxes. This discussion also does not address the special tax rules applicable to particular non-U.S. holders, including, without limitation:

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In addition, this discussion does not address the tax treatment of partnerships (or entities or arrangements that are treated as partnerships for U.S. federal income tax purposes) or persons that hold their common stock through partnerships. If a partnership, including any entity or arrangement treated as a partnership for U.S. federal income tax purposes, holds shares of our common stock, the U.S. federal income tax treatment of a partner in such partnership will generally depend upon the status of the partner and the activities of the partnership. Such partners and partnerships should consult their tax advisors regarding the tax consequences of the purchase, ownership and disposition of our common stock.

There can be no assurance that a court or the IRS will not challenge one or more of the tax consequences described herein, and we have not obtained, nor do we intend to obtain, a ruling or opinion of counsel with respect to the U.S. federal income tax consequences to a non-U.S. holder of the purchase, ownership, or disposition of our common stock.

THIS DISCUSSION IS FOR INFORMATION PURPOSES ONLY AND IS NOT INTENDED AS TAX ADVICE. PROSPECTIVE INVESTORS ARE URGED TO CONSULT THEIR TAX ADVISORS WITH RESPECT TO THE APPLICATION OF THE U.S. FEDERAL INCOME TAX LAWS TO THEIR PARTICULAR SITUATION, AS WELL AS ANY TAX CONSIDERATIONS RELATING TO THE ACQUISITION, OWNERSHIP AND DISPOSITION OF OUR COMMON STOCK ARISING UNDER THE U.S. FEDERAL ESTATE OR GIFT TAX LAWS OR UNDER THE LAWS OF ANY STATE, LOCAL, NON-U.S. OR OTHER TAXING JURISDICTION OR UNDER ANY APPLICABLE INCOME TAX TREATY.

Distributions on Our Common Stock

Distributions, if any, on our common stock generally will constitute dividends for U.S. federal income tax purposes to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. If a distribution exceeds our current and accumulated earnings and profits, the excess will be treated as a tax-free return of the non-U.S. holder's investment, up to such holder's adjusted tax basis in the common stock. Any remaining excess will be treated as capital gain from the sale or exchange of such common stock, subject to the tax treatment described below in "Gain on Sale, Exchange or Other Disposition of Our Common Stock." Any such distribution will also be subject to the discussion below under the heading "Withholding Requirements Under FATCA."

In general, dividends paid to a non-U.S. holder will be subject to withholding of U.S. federal income tax at a 30% rate of the gross amount of the dividend or such lower rate as may be specified by an applicable income tax treaty. A non-U.S. holder who claims the benefit of an applicable income tax treaty generally will be required to satisfy certain certification and other requirements. Such non-U.S. holders must generally provide us and/or the applicable withholding agent, with a properly completed and executed IRS Form W-8BEN or IRS Form W-8BEN-E (or other appropriate form)

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certifying qualification for an exemption from or reduction in withholding under an applicable income tax treaty. Such certification must be provided before the payment of dividends and must be updated periodically.

Dividends paid to a non-U.S. holder that are effectively connected with the non-U.S. holder's conduct of a trade or business in the United States (and, if required by an applicable income tax treaty, are treated as attributable to a permanent establishment maintained by the non- U.S. holder in the United States) generally will be taxed on a net income basis at the regular rates. Such effectively connected dividends will not be subject to the U.S. withholding tax described above if the non-U.S. holder satisfies certain certification requirements by providing us and/or the applicable withholding agent a properly executed IRS Form W-8ECI certifying eligibility for exemption. If the non-U.S. holder is a non-U.S. corporation, it may also be subject to a branch profits tax (at a 30% rate or such lower rate as specified by an applicable income tax treaty) on such effectively connected dividends (as adjusted for certain items).

If tax is withheld in an amount in excess of the amount applicable under an income tax treaty (including as a result of a non-U.S. holder failing to timely furnish any certification described above), a refund of the excess amount may generally be obtained by a non-U.S. holder by timely filing an appropriate claim for refund with the IRS. Non-U.S. holders should consult their tax advisors regarding their entitlement to benefits under an applicable income tax treaty.

Gain on Sale, Exchange or Other Disposition of Our Common Stock

Subject to the discussion below regarding backup withholding and foreign accounts, in general, a non-U.S. holder will not be subject to any U.S. federal income tax on any gain realized upon such holder's sale, exchange or other disposition of shares of our common stock unless:

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Backup Withholding and Information Reporting

We (or the applicable paying agent) must report annually to the IRS and to each non-U.S. holder the gross amount of the distributions on our common stock paid to such holder and the tax withheld, if any, with respect to such distributions. A non-U.S. holder may have to comply with specific certification procedures to establish that the holder is not a U.S. person (as defined in the Code) in order to avoid backup withholding at the applicable rate (currently at a rate of 24%) with respect to dividends on our common stock. A non-U.S. holder generally will not be subject to U.S. backup withholding with respect to payments of dividends on our common stock if it certifies its non-U.S. status by providing a valid IRS Form W-8BEN, W-8BEN-E, W-8ECI, or other applicable IRS Form W-8, or otherwise establishes an exemption, provided the payor does not have actual knowledge or reason to know such non-U.S. holder is a United States person. Distributions paid to non-U.S. holders that are subject to the U.S. withholding tax, as described above in "Distributions on Our Common Stock," generally will be exempt from U.S. backup withholding.

Information reporting and backup withholding will generally apply to the proceeds of a disposition of our common stock by a non-U.S. holder effected by or through the U.S. office of any broker, U.S. or foreign, unless the holder establishes an exemption by certifying its status as a non-United States person and satisfies certain other requirements, or otherwise establishes an exemption. Generally, information reporting and backup withholding will not apply to a payment of disposition proceeds to a non-U.S. holder where the transaction is effected outside the United States through a non-U.S. office of a broker. However, for information reporting purposes, dispositions effected through a non-U.S. office of a broker with substantial U.S. ownership or operations generally will be treated in a manner similar to dispositions effected through a U.S. office of a broker. Non-U.S. holders should consult their tax advisors regarding the application of the information reporting and backup withholding rules to them.

Copies of information returns may be made available to the tax authorities of the country in which the non-U.S. holder resides or is incorporated under the provisions of a specific treaty or agreement. Any documentation provided to an applicable withholding agent may need to be updated in certain circumstances.

Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules from a payment to a non-U.S. holder may be allowed as a credit against the non-U.S. holder's U.S. federal income tax liability, if any, and may entitle such holder to a refund, provided that the required information is timely furnished to the IRS.

Withholding Requirements Under FATCA

Sections 1471 through 1474 of the Code and the Treasury Regulations and other administrative guidance issued thereunder (commonly referred to as the Foreign Account Tax Compliance Act, or "FATCA") generally impose a U.S. federal withholding tax of 30% on dividends on our common stock and, subject to the proposed Treasury Regulations discussed below, the gross proceeds from a sale or other disposition of our common stock paid to a "foreign financial institution" (as specifically defined for this purpose) and certain other non-U.S. entities unless various U.S. information reporting and due diligence requirements (generally relating to ownership by U.S. persons of interests in or accounts with those entities) have been satisfied, or an exemption applies. An intergovernmental agreement between the United States and an applicable foreign country may modify these requirements. The U.S. Treasury released proposed Treasury Regulations which, if finalized in their present form, would eliminate the federal withholding tax of 30% applicable to the gross proceeds of a sale or other disposition of our common stock. Taxpayers may generally rely on the proposed regulations until final regulations are issued. Non-U.S. holders should consult their tax advisors regarding the effects of FATCA on their investment in our common stock.

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THIS SUMMARY IS NOT INTENDED TO BE TAX ADVICE. EACH PROSPECTIVE INVESTOR SHOULD CONSULT ITS TAX ADVISOR REGARDING THE PARTICULAR U.S. FEDERAL, STATE AND LOCAL AND NON-U.S. TAX CONSEQUENCES OF PURCHASING, OWNING AND DISPOSING OF OUR COMMON STOCK, INCLUDING THE CONSEQUENCES OF ANY PROPOSED CHANGE IN APPLICABLE LAWS.

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UNDERWRITING

William Blair & Company, L.L.C. and Craig-Hallum Capital Group LLC are acting as representatives of the several underwriters (the "Representatives"). Subject to the terms and conditions set forth in an underwriting agreement among us and the Representatives, we have agreed to sell to the underwriters, and each underwriter has severally agreed to purchase, at the public offering price less the underwriting discounts and commissions set forth on the cover page of this prospectus, the number of shares of common stock listed next to its name in the following table:

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The underwriters are committed to purchase all the common shares offered by us if they purchase any shares. The underwriting agreement also provides that if an underwriter defaults, the purchase commitments of non-defaulting underwriters may also be increased or the offering may be terminated.

The underwriters propose to offer the common shares directly to the public at the public offering price set forth on the cover page of this prospectus and to certain dealers at that price less a concession not in excess of $0.69 per share. After the initial offering of the shares to the public, if all of the common shares are not sold at the public offering price, the underwriters may change the offering price and the other selling terms. Sales of shares made outside of the United States may be made by affiliates of the underwriters. The offering of the shares by the underwriters is subject to receipt and acceptance and subject to the underwriters' right to reject any order in whole or in part.

We have agreed to indemnify the several underwriters against certain liabilities, including liabilities under the Securities Act, relating to losses or claims resulting from material misstatements in or omissions from this prospectus supplement, the registration statement of which this prospectus supplement is a part, certain free writing prospectuses that may be used in the offering and in any marketing materials used in connection with this offering and to contribute to payments the underwriters may be required to make in respect of those liabilities.

Option to Purchase Additional Shares

We have granted to the underwriters an option, exercisable for 30 calendar days from the date of this prospectus supplement, to purchase up to 652,000 additional shares of common stock at the public offering price listed on the cover of this prospectus supplement, less underwriting discounts and commissions. Any shares issued or sold under the option will be issued and sold on the same terms and conditions as the other shares that are the subject of this offering.

Underwriting Discounts and Expenses

The underwriting fee is equal to the public offering price per share of common stock less the amount paid by the underwriters to us per share of common stock. The underwriting fee is $1.15 per share. The following table shows the per share and total underwriting discounts and commissions to be paid to the underwriters assuming both no exercise and full exercise of the underwriters' option to purchase additional shares.

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We estimate that the total expenses of this offering, including registration, filing and listing fees, printing fees and legal and accounting expenses, but excluding the underwriting discounts and commissions, will be approximately $350,000. We have agreed to reimburse the underwriters for certain of their expenses up to $25,000.

Electronic Distribution

A prospectus in electronic format may be made available on the web sites maintained by one or more underwriters, or selling group members, if any, participating in the offering. The underwriters may agree to allocate a number of shares to underwriters and selling group members for sale to their online brokerage account holders. Internet distributions will be allocated by the representatives to underwriters and selling group members that may make Internet distributions on the same basis as other allocations.

Lock-Up

We have agreed with the Representatives, through and including the date that is 90 days after the date of this prospectus supplement and subject to specified exceptions, not to (i) offer, sell, contract to sell, pledge, grant any option to purchase, make any short sale or otherwise transfer or dispose of, directly or indirectly, or file with the SEC a registration statement under the Securities Act relating to, any shares of our common stock or any securities that are substantially similar to our common stock, including but not limited to any options to purchase shares of our common stock or any securities that are convertible into or exchangeable for, or that represent the right to receive, common stock or any such substantially similar securities, or publicly disclose the intention to make any offer, sale, pledge, disposition or filing or (ii) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of our common stock, or any such other securities, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of our common stock or such other securities, in cash or otherwise, without the prior written consent of the Representatives.

Our directors and executive officers have agreed with the Representatives, subject to specified exceptions, not to, without the prior written consent of the Representatives, (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, make any short sale or otherwise transfer or dispose of, directly or indirectly, any shares of our common stock or any securities convertible into, exercisable or exchangeable for or that represent the right to receive our common stock (including without limitation, our common stock which may be deemed to be beneficially owned in accordance with the rules and regulations of the SEC and securities which may be issued upon exercise of a stock option or warrant), whether now owned or hereafter acquired, (ii) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of our common stock, whether any such transaction is to be settled by delivery of our common stock or such other securities, in cash or otherwise, (iii) make any demand for, or exercise any right with respect to, the registration under the Securities Act of any of our common stock or any security convertible into or exercisable or exchange for our common stock or (iv) publicly disclose the intention to do any of the foregoing. These restrictions will apply through and including the date that is 90 days after the date of this prospectus supplement.

Listing

Our common stock is listed on the New York Stock Exchange under the symbol "MEC."

Price Stabilization and Short Positions

Until the distribution of the shares is completed, SEC rules may limit the underwriters and selling group members from bidding for and purchasing shares of our common stock. However, the underwriters may engage in transactions that stabilize the price of our common stock, such as bids or purchases to peg, fix or maintain that price.

In connection with this offering, the underwriters may purchase and sell shares of our common stock in the open market. These transactions may include short sales, purchases on the open market to cover positions created by short sales and stabilizing transactions. Short sales involve the sale by the underwriters of a greater number of shares than it is required to purchase in this offering. "Covered" short sales are sales made in an amount not greater than the

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underwriters' option to purchase additional shares described above. The underwriters may close out any covered short position by either exercising this option or purchasing shares in the open market. In determining the source of shares to close out the covered short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared to the price at which they may purchase shares through this option. "Naked" short sales are sales in excess of this option. The underwriters must close out any naked short position by purchasing shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of our common stock in the open market after pricing that could adversely affect investors who purchase in this offering. Stabilizing transactions consist of various bids for or purchases of shares of our common stock made by the underwriters in the open market prior to the closing of this offering.

Similar to other purchase transactions, the underwriters' purchases to cover short sales may have the effect of raising or maintaining the market price of our common stock or preventing or retarding a decline in the market price of our common stock. As a result, the price of our common stock may be higher than the price that might otherwise exist in the open market. The underwriters may conduct these transactions on the New York Stock Exchange, in the over-the-counter market or otherwise.

Neither we nor the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of our common stock. In addition, neither we nor the underwriters make any representation that the underwriters will engage in these transactions or that these transactions, once commenced, will not be discontinued without notice.

Electronic Offer, Sale and Distribution of Shares

In connection with this offering, the underwriters or securities dealers may distribute prospectuses by electronic means, such as e-mail. In addition, the underwriters may facilitate Internet distribution for this offering to certain of their respective Internet subscription customers. The underwriters may allocate a limited number of shares for sale to their respective online brokerage customers. An electronic prospectus is available on the Internet websites maintained by the several underwriters. The information on the websites of such underwriters is not part of this prospectus supplement.

Other Relationships

The underwriters and their respective affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. The underwriters and their respective affiliates may engage in from time to time in the future certain investment banking and other commercial dealings in the ordinary course of business with us or our affiliates, for which they have received and may continue to receive customary fees and commissions.

In the ordinary course of their various business activities, the underwriters and their respective affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers, and such investment and securities activities may involve securities and/or instruments of the issuer. The underwriters and their respective affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Selling Restrictions

Notice to Prospective Investors in the European Economic Area

In relation to each Member State of the European Economic Area (each a "Relevant State"), no shares of our common stock have been offered or will be offered pursuant to this offering to the public in that Relevant State prior to the publication of a prospectus in relation to the shares of our common stock which has been approved by the competent authority in that Relevant State or, where appropriate, approved in another Relevant State and notified to the competent

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authority in that Relevant State, all in accordance with the Prospectus Regulation, except that the shares of our common stock may be offered to the public in that Relevant State at any time:

provided that no such offer of the shares of common stock shall require us or any underwriter to publish a prospectus pursuant to Article 3 of the Prospectus Regulation, supplement a prospectus pursuant to Article 23 of the Prospectus Regulation or publish an Annex IX document pursuant to Article 1(4) of the Prospectus Regulation.

For the purposes of this provision, the expression an "offer to the public" in relation to the shares of our common stock in any Relevant State means the communication in any form and by any means of sufficient information on the terms of the offer and any shares of our common stock to be offered so as to enable an investor to decide to purchase any shares of our common stock, and the expression "Prospectus Regulation" means Regulation (EU) 2017/1129.

Notice to Prospective Investors in the United Kingdom

No shares of our common stock have been offered or will be offered pursuant to this offering to the public in the United Kingdom except that the shares of our common stock may be offered to the public in the United Kingdom at any time:

For the purposes of this provision, the expression an "offer to the public" in relation to the shares of our common stock in the United Kingdom means the communication to any person which presents sufficient information on: (a) the shares of Class A common stock to be offered; and (b) the terms on which they are to be offered, to enable an investor to decide to buy or subscribe for the shares of Class A common stock and the expressions "POATR" means the Public Offers and Admissions to Trading Regulations 2024.

Each person in the United Kingdom who receives any communication in respect of, or who acquires any of our shares of common stock under, the offers to the public contemplated in this prospectus, or to whom our shares of common stock are otherwise made available, will be deemed to have represented, warranted, acknowledged, and agreed to and with us, the underwriters, and their respective affiliates that it meets the criteria outlined in this section.

Notice to Prospective Investors in France

Neither this prospectus nor any other offering material relating to the shares of our common stock described in this prospectus has been submitted to the clearance procedures of the Autorité des Marchés Financiers or of the competent authority of another member state of the European Economic Area and notified to the Autorité des Marchés

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Financiers. The shares of our common stock have not been offered or sold and will not be offered or sold, directly or indirectly, to the public in France. Neither this prospectus nor any other offering material relating to the shares of our common stock has been or will be:

Such offers, sales and distributions will be made in France only:

The shares of our common stock may be resold directly or indirectly, only in compliance with articles L.411-1, L.411-2, L.412-1 and L.621-8 through L.621-8-3 of the French Code monétaire et financier.

Notice to Prospective Investors in Hong Kong

The shares of common stock may not be offered or sold in Hong Kong by means of any document other than (i) in circumstances which do not constitute an offer to the public within the meaning of the Companies (Winding Up and Miscellaneous Provisions) Ordinance (Cap. 32, Laws of Hong Kong), or (ii) to "professional investors" within the meaning of the Securities and Futures Ordinance (Cap. 571, Laws of Hong Kong) and any rules made thereunder, or (iii) in other circumstances which do not result in the document being a "prospectus" within the meaning of the Companies (Winding Up and Miscellaneous Provisions) Ordinance (Cap. 32, Laws of Hong Kong) and no advertisement, invitation or document relating to the shares of common stock may be issued or may be in the possession of any person for the purpose of issue (in each case whether in Hong Kong or elsewhere), which is directed at, or the contents of which are likely to be accessed or read by, the public in Hong Kong (except if permitted to do so under the laws of Hong Kong) other than with respect to shares of common stock which are or are intended to be disposed of only to persons outside Hong Kong or only to "professional investors" within the meaning of the Securities and Futures Ordinance (Cap. 571, Laws of Hong Kong) and any rules made thereunder.

Notice to Investors in Switzerland

The shares of our common stock may not be publicly offered in Switzerland and will not be listed on the SIX Swiss Exchange ("SIX") or on any other stock exchange or regulated trading facility in Switzerland. This document has been prepared without regard to the disclosure standards for issuance prospectuses under art. 652a or art. 1156 of the Swiss Code of Obligations or the disclosure standards for listing prospectuses under art. 27 ff. of the SIX Listing Rules or the listing rules of any other stock exchange or regulated trading facility in Switzerland. Neither this document nor any other offering or marketing material relating to the shares or the offering may be publicly distributed or otherwise made publicly available in Switzerland.

Neither this prospectus nor any other offering or marketing material relating to the offering, us, or the shares of Class A common stock have been or will be filed with or approved by any Swiss regulatory authority. In particular, this prospectus will not be filed with, and the offer of shares of our common stock will not be supervised by, FINMA, and the

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offer of shares of our common stock has not been and will not be authorized under CISA. The investor protection afforded to acquirers of interests in collective investment schemes under the CISA does not extend to acquirers of shares of our common stock.

Notice to Prospective Investors in Canada

The shares of our common stock may be sold in Canada only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the shares of our common stock must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser's province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser's province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 of National Instrument 33-105 Underwriting Conflicts (NI 33-105), the underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

Notice to Prospective Investors in Australia

No placement document, prospectus, product disclosure statement, or other disclosure document has been lodged with the Australian Securities and Investments Commission in relation to this offering. This prospectus does not constitute a prospectus, product disclosure statement, or other disclosure document under Chapter 6D.2 of the Corporations Act 2001 (the "Corporations Act"), and does not purport to include the information required for a prospectus, product disclosure statement, or other disclosure document under the Corporations Act.

Any offer in Australia of the shares may only be made to persons, or the Exempt Investors, who are "sophisticated investors" (within the meaning of section 708(8) of the Corporations Act), "professional investors" (within the meaning of section 708(11) of the Corporations Act), or otherwise pursuant to one or more exemptions contained in section 708 of the Corporations Act so that it is lawful to offer the shares without disclosure to investors under Chapter 6D of the Corporations Act.

The shares applied for by Exempt Investors in Australia must not be offered for sale in Australia in the period of 12 months after the date of allotment under the offering, except in circumstances where disclosure to investors under Chapter 6D of the Corporations Act would not be required pursuant to an exemption under section 708 of the Corporations Act or otherwise, or where the offer is pursuant to a disclosure document which complies with Chapter 6D of the Corporations Act. Any person acquiring shares must observe such Australian on-sale restrictions.

This prospectus contains general information only and does not take account of the investment objectives, financial situation, or particular needs of any particular person. It does not contain any securities recommendations or financial product advice. Before making an investment decision, investors need to consider whether the information in this prospectus is appropriate to their needs, objectives, and circumstances, and, if necessary, seek expert advice on those matters.

Notice to Prospective Investors in Japan

The shares of our common stock have not been and will not be registered under the Financial Instruments and Exchange Act of Japan (Act No. 25 of 1948, as amended; the "FIEA") and no shares of our common stock will be offered or sold, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan (which term as used

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herein means any person "resident" in Japan, including any corporation or other entity organized under the laws of Japan), or to others for re-offering or resale, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan except pursuant to an exemption from the registration requirements of, and otherwise in compliance with, the FIEA and any other applicable laws, regulations and ministerial guidelines of Japan in effect at the relevant time.

Notice to Prospective Investors in Singapore

This prospectus has not been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the shares of our common stock may not be circulated or distributed, nor may the shares be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor (as defined under Section 4A of the Securities and Futures Act, Chapter 289 of Singapore (the "SFA")) under Section 274 of the SFA, (ii) to a relevant person (as defined in Section 275(2) of the SFA) pursuant to Section 275(1) of the SFA, or any person pursuant to Section 275(1A) of the SFA, and in accordance with the conditions specified in Section 275 of the SFA, or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA, in each case subject to conditions set forth in the SFA.

Where the shares of our common stock are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

the securities (as defined in Section 239(1) of the SFA) of that corporation shall not be transferable for six months after that corporation has acquired the shares under Section 275 of the SFA except:

Singapore Securities and Futures Act Product Classification-Solely for the purposes of its obligations pursuant to Sections 309B(1)(a) and 309B(1)(c) of the SFA, we have determined, and hereby notify all relevant persons (as defined in Section 309A of the SFA) that the shares of Class A common stock are prescribed capital markets products (as defined in the Securities and Futures (Capital Markets Products) Regulations 2018) and Excluded Investment Products (as defined in MAS Notice SFA 04-N12: Notice on the Sale of Investment Products and MAS Notice FAA-N16: Notice on Recommendations on Investment Products).

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LEGAL MATTERS

The validity of the shares of common stock offered hereby will be passed upon for us by Foley & Lardner LLP, Milwaukee, Wisconsin. The underwriters are being represented in connection with this offering by Latham & Watkins LLP, Chicago, Illinois.

EXPERTS

The financial statements of Mayville Engineering Company, Inc. as of December 31, 2025 and 2024, and for each of the three years in the period ended December 31, 2025, incorporated in this prospectus supplement by reference to the Form 10-K filed on March 4, 2026, have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report. Such financial statements are incorporated by reference in reliance upon the report of such firm, given their authority as experts in accounting and auditing.

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WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC's website at www.sec.gov. Copies of certain information filed by us with the SEC are also available on our website at https://www.mecinc.com/. Our website is not a part of this prospectus supplement and the information contained on, or accessible through, our website is not incorporated by reference in this prospectus supplement.

This prospectus supplement and the accompanying prospectus are part of a registration statement we filed with the SEC. This prospectus supplement and the accompanying prospectus omit some information contained in the registration statement in accordance with SEC rules and regulations. You should review the information and exhibits in the registration statement for further information about us and our consolidated subsidiaries and the securities we are offering. Statements in this prospectus supplement and the accompanying prospectus concerning any document we filed as an exhibit to the registration statement or that we otherwise filed with the SEC are not intended to be comprehensive and are qualified by reference to these filings and the exhibits attached thereto. You should review the complete document to evaluate these statements.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to incorporate by reference much of the information we file with the SEC, which means that we can disclose important information to you by referring you to those publicly available documents. The information that we incorporate by reference in this prospectus supplement and the accompanying prospectus and information in documents that we file later with the SEC will automatically update and supersede information contained in documents filed earlier with the SEC or contained in this prospectus or a prospectus supplement. We incorporate by reference in this prospectus the documents listed below:

In addition, we incorporate by reference in this prospectus supplement and the accompanying prospectus any future filings that we may make with the SEC under Sections 13(a), 13(c), 14, or 15(d) of the Exchange Act, prior to the termination of the offering under this prospectus supplement and the accompanying prospectus. These documents may include annual, quarterly and current reports, as well as proxy statements. Notwithstanding the foregoing, we are not incorporating any document or information deemed to have been furnished and not filed in accordance with SEC rules. You may obtain a copy of any or all of the documents referred to above which may have been or may be incorporated by reference into this prospectus supplement and the accompanying prospectus (excluding certain exhibits to the documents) at no cost to you by writing or telephoning us at the following address:

Mayville Engineering Company, Inc.

Attention: Sean Leuba

135 S. 84^th Street, Suite 300

Milwaukee, Wisconsin 53214

(414) 381-2860

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Prospectus

Mayville Engineering Company, Inc.

$100,000,000

Debt Securities

Common Stock

Preferred Stock

Warrants

Purchase Contracts

Purchase Units

Units

We may offer and sell from time to time these securities in one or more classes or series and in amounts, at prices and on terms that we will determine at the time of one or more offerings, up to $100,000,000 in aggregate offering price.

This prospectus provides you with a general description of the securities we may offer. Each time we sell securities, we will provide a prospectus supplement that will contain the specific terms of the securities offered. Each prospectus supplement will also describe the specific manner in which we will offer the securities. Each prospectus supplement may also add, update or change information contained in this prospectus. You should read this prospectus and the applicable prospectus supplement, as well as the documents incorporated by reference in this prospectus and the applicable prospectus supplement, carefully before you invest.

The securities may be offered and sold on a continuous or delayed basis to or through underwriters, brokers, dealers or agents as designated from time to time, or directly to one or more other purchasers or through a combination of such methods. See "Plan of Distribution." If any underwriters, dealers or agents are involved in the sale of any of the securities, their names, and any applicable purchase price, fee, commission or discount arrangements between or among them, will be set forth, or will be calculable from the information set forth, in the applicable prospectus supplement.

This prospectus may not be used to offer and sell securities unless accompanied by a prospectus supplement.

Our common stock is traded on the New York Stock Exchange under the symbol "MEC."

Investment in our securities involves risks. See "Risk Factors" on page 2 of this prospectus, in any applicable prospectus supplement and in the documents incorporated by reference in this prospectus and the applicable prospectus supplement for a discussion of certain factors which should be considered in an investment in the securities which may be offered hereby.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is May 20, 2024.

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ABOUT THIS PROSPECTUS

All references to "MEC," the "Company," "we," "us" and "our" in this prospectus mean, unless we otherwise indicate or the context indicates otherwise, Mayville Engineering Company, Inc. together with its consolidated subsidiaries. All references in this prospectus to our consolidated financial statements include, unless the context indicates otherwise, the related notes.

This prospectus is part of a registration statement that we filed with the United States Securities and Exchange Commission (the "SEC") utilizing a "shelf" registration process. Under this shelf registration process, we may, from time to time, sell the securities or any combination of the securities described in this prospectus in one or more offerings.

Each time we sell securities, we will provide a prospectus supplement or other type of offering document, supplement or material (together referred to herein as a "prospectus supplement") that will contain specific information about the terms of that offering. The prospectus supplement may also add, update or change information contained in this prospectus. Therefore, if there is any inconsistency between the information contained or incorporated by reference in this prospectus and the prospectus supplement, you should rely on the information in the prospectus supplement (including any information incorporated by reference therein). You should read this prospectus and the applicable prospectus supplement together with the additional information described under the heading "Where You Can Find More Information."

The registration statement that contains this prospectus, including the exhibits to the registration statement and the documents incorporated by reference herein, contains additional information about us and the securities offered under this prospectus. That registration statement can be read at the SEC website mentioned under the heading "Where You Can Find More Information."

You should rely only on the information contained or incorporated by reference in this prospectus and in any prospectus supplement. "Incorporated by reference" means that we can disclose important information to you by referring you to another document filed separately with the SEC. We have not authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not making offers to sell or solicitations to buy the securities in any jurisdiction in which an offer or solicitation is not authorized or in which the person making that offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation. You should not assume that the information in this prospectus or any prospectus supplement, as well as the information we file or previously filed with the SEC that we incorporate by reference in this prospectus or any prospectus supplement, is accurate as of any date other than its respective date. Our business, financial condition, results of operations and prospects may have changed since those dates.

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

Certain matters discussed or incorporated by reference into this prospectus contain forward-looking statements that involve risks and uncertainties, such as statements related to future events, business strategy, future performance, future operations, financial position, estimated revenues and losses, projected costs, prospects, plans and objectives of management. All statements other than statements of historical fact may be forward-looking statements. Forward-looking statements are often, but not always, identified by the use of words such as "seek," "anticipate," "plan," "continue," "estimate," "expect," "may," "will," "project," "predict," "potential," "targeting," "intend," "could," "might," "should," "believe" and similar expressions or their negative. Forward-looking statements should not be read as a guarantee of future performance or results, and will not necessarily be accurate indications of the times at, or by, which such performance or results will be achieved. Forward-looking statements are based on management's belief, based on currently available information, as to the outcome and timing of future events. These statements involve estimates, assumptions, known and unknown risks, uncertainties and other factors that may cause actual results or events to differ materially from those expressed in such forward-looking statements. We believe the expectations reflected in the forward-looking statements contained in or incorporated by reference into this prospectus are reasonable, but no assurance can be given that these expectations will prove to be correct. Forward-looking statements should not be unduly relied upon.

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Important factors that could cause actual results or events to differ materially from those expressed in forward-looking statements include, but are not limited to, the following:

These factors are not necessarily all of the important factors that could cause actual results or events to differ materially from those expressed in forward-looking statements. Other unknown or unpredictable factors could also cause

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actual results or events to differ materially from those expressed in the forward-looking statements. All forward-looking statements attributable to us are qualified in their entirety by this cautionary statement. Forward-looking statements speak only as of the date hereof. We undertake no obligation to update or revise any forward-looking statements after the date on which any such statement is made, whether as a result of new information, future events or otherwise, except as required by federal securities laws.

RISK FACTORS

Investing in our securities involves risk. Before you decide whether to purchase any of our securities, in addition to the other information, documents or reports included in or incorporated by reference into this prospectus and any accompanying prospectus supplement, you should carefully consider the risk factors in the section entitled "Risk Factors" in any prospectus supplement as well as our most recent Annual Report on Form 10-K and the other reports we file with the SEC, which are incorporated by reference into this prospectus and any prospectus supplement in their entirety, as the same may be amended, supplemented or superseded from time to time by our filings under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). The risks and uncertainties described in our SEC filings are not the only ones facing us. Additional risks and uncertainties not presently known to us, or that we currently see as immaterial, may also harm our business. If any such risks and uncertainties actually occur, our business, results of operations and financial condition could be materially and adversely affected, the market price of our securities could decline, and you could lose all or part of your investment.

MAYVILLE ENGINEERING COMPANY, INC.

MEC is a leading U.S.-based, vertically-integrated, value-added manufacturing partner providing a full suite of manufacturing solutions from concept to production, including design, prototyping and tooling, fabrication, aluminum extrusion, coating, assembly and aftermarket components. Our customers operate in diverse end markets, including heavy- and medium-duty commercial vehicles, construction & access equipment, powersports, agriculture, military and other end markets. Founded in 1945 and headquartered in Milwaukee, Wisconsin, we are a leading Tier I U.S. supplier of highly engineered components to original equipment manufacturer customers with leading positions in their respective markets. The Company operates 23 facilities located in Arkansas, Michigan, Mississippi, Ohio, Pennsylvania, Virginia, and Wisconsin. Our engineering expertise and technical know-how allow us to add value through every product redevelopment cycle (generally every three to five years for our customers).

We are a Wisconsin corporation, and our principal executive offices are located at 135 South 84th Street, Suite 300, Milwaukee, Wisconsin 53214. Our telephone number is (414) 381-2860.

USE OF PROCEEDS

We intend to use the net proceeds from the sale of the securities as set forth in the applicable prospectus supplement.

DESCRIPTION OF CAPITAL STOCK

Our amended and restated articles of incorporation provide that we have the authority to issue 75,000,000 shares of our common stock, no par value per share, and 5,000,000 shares of preferred stock, par value $0.01 per share. The following is a summary of the material provisions of our common stock and preferred stock. This summary does not purport to be complete and is qualified in its entirety by reference to applicable Wisconsin law and our amended and restated articles of incorporation and bylaws, which are incorporated by reference as exhibits to this registration statement.

Corporate Governance

We are a corporation organized under the laws of the state of Wisconsin and are governed by the Wisconsin Business Corporation Law (the "WBCL"), our amended and restated articles of incorporation and our bylaws.

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Common Stock

As of February 16, 2024, we had 20,364,907 shares of common stock issued and outstanding.

Holders of our common stock are entitled to one vote for each share held on all matters submitted to a vote of shareholders. Accordingly, holders of a majority of the shares of our common stock entitled to vote in any election of directors may elect all of the directors standing for election. Holders of our common stock are entitled to receive proportionately any dividends if and when such dividends are declared by our board of directors, subject to any preferential dividend rights of outstanding preferred stock. Upon the liquidation, dissolution or winding up of the Company, the holders of our common stock are entitled to receive ratably net assets available after the payment of all debts and other liabilities and subject to the prior rights of holders of any outstanding preferred stock. The rights, preferences and privileges of holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that we may designate and issue in the future.

The transfer agent for our common stock is American Stock Transfer & Trust Co.

Preferred Stock

Under the terms of our amended and restated articles of incorporation, which we sometimes refer to as the articles, the board of directors are authorized to designate and issue up to 5,000,000 shares of preferred stock in one or more series without shareholder approval. Our board of directors have discretion to determine the rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences, of each series of preferred stock.

It is not possible to state the actual effect of the issuance of any shares of preferred stock upon the rights of holders of our common stock until the board of directors determines the specific rights of the holders of the preferred stock. However, these effects might include:

At present, there are no shares of preferred stock outstanding.

Dividends and Other Distributions

The holders of our common stock will be entitled to receive proportionately any cash or stock dividends if and when such dividends are declared by the board of directors, subject to any preferential dividend rights of outstanding preferred stock. In the event of the dissolution or liquidation of the Company, after the full preferential rights, if any, on any outstanding preferred stock has been paid to or set aside for the holders of such preferred stock, the holders of our common stock will be entitled to receive proportionately all of our remaining assets.

The declaration and payment of any dividend will be subject to the discretion of our board of directors. The time and amount of any dividend will be dependent upon our financial condition, operations, cash requirements and availability, debt repayment obligations, capital expenditure needs, restrictions in our debt instruments, industry trends and any other factors our board of directors may consider relevant.

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Removal of Directors

Our articles provide that any director may be removed from office, but only for cause by the affirmative vote of shareholders holding at least 66 2/3% of the then outstanding shares of stock entitled to vote in the election of directors. However, if at least two-thirds of the directors then in office plus one director recommend removal of a director, that director may be removed without cause by the affirmative vote of a majority of the outstanding shares. "Cause" is construed to exist only if the director whose removal is proposed has been convicted of a felony or has been adjudged to be liable for willful misconduct in the performance of his or her duties to us in a matter which has a material adverse effect on our business.

Voting by Shareholders

Each holder of our common stock is entitled to one vote per share for the election of directors and for all other corporate purposes.

Amendment of Articles

The WBCL allows us to amend our articles at any time to add or change a provision that is required or permitted to be included in the articles of incorporation or to delete a provision that is not required to be included in the articles of incorporation. Our board of directors can propose one or more amendments for submission to shareholders and may condition its submission of the proposed amendment on any basis if it provides certain notice and includes certain information regarding the proposed amendment in that notice. The provisions in our articles relating to (a) the structure of the board and (b) certain amendments to the bylaws may only be amended by the approval of 66 2/3% of the then outstanding shares entitled to vote.

Amendment of Bylaws

Our bylaws may be amended or repealed and new bylaws may be adopted by our shareholders at any annual or special meeting at which a quorum is present. The bylaws may also be amended or repealed and new bylaws may be adopted by our board of directors by affirmative vote of a majority of the number of directors present at any meeting at which a quorum is in attendance; provided, however, that the shareholders in adopting, amending or repealing a particular bylaw may provide therein that our board of directors may not amend, repeal or readopt that bylaw. Notwithstanding the foregoing, pursuant to our articles, the provisions of our bylaws relating to the general powers, number, classification, tenure and qualifications of the directors may be amended or repealed only by the affirmative vote of shareholders holding at least 66 2/3% of the then outstanding shares of all classes of our capital stock, voting together as a single class; provided, however, that our board of directors can amend or repeal such provisions by resolution adopted by at least two-thirds of the directors then in office plus one director, without a vote of the shareholders.

Anti-Takeover Effects of Various Provisions of Wisconsin Law, Our Amended and Restated Articles of Incorporation, Our Bylaws and Our Amended and Restated Credit Agreement

Provisions of Wisconsin law have certain anti-takeover effects. Our amended and restated articles of incorporation and bylaws also contain provisions that may have similar effects.

Wisconsin Anti-Takeover Statutes

Sections 180.1140 to 180.1144 of the WBCL restrict a broad range of business combinations between a Wisconsin corporation and an "interested stockholder" for a period of three years unless specified conditions are met. The WBCL defines a "business combination" as including certain mergers or share exchanges, sales of assets, issuances of stock or rights to purchase stock and other related party transactions. An "interested stockholder" is a person who beneficially owns, directly or indirectly, 10% of the outstanding voting stock of a corporation or who is an affiliate or associate of the corporation and beneficially owned 10% of the voting stock within the last three years. During the initial three-year period after a person becomes an interested stockholder in a Wisconsin corporation, with some exceptions, the

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WBCL prohibits a business combination with the interested stockholder unless the corporation's board of directors approved the business combination or the acquisition of the stock by the interested stockholder prior to the acquisition date. Following this three-year period, the WBCL also prohibits a business combination with an interested stockholder unless:

Sections 180.1130 to 180.1133 of the WBCL govern certain mergers or share exchanges between public Wisconsin corporations and significant shareholders, and sales of all or substantially all of the assets of public Wisconsin corporations to significant shareholders. These transactions must be approved by 80% of all shareholders and two-thirds of shareholders other than the significant shareholder, unless the shareholders receive a statutory "fair price." Section 180.1130 of the WBCL generally defines a "significant shareholder" as the beneficial owner of 10% or more of the voting power of the outstanding voting shares, or an affiliate of the corporation who beneficially owned 10% or more of the voting power of the then outstanding shares within the last two years.

Section 180.1150 of the WBCL provides that in particular circumstances the voting power of shares of a public Wisconsin corporation held by any person in excess of 20% of the voting power is limited to 10% of the voting power these excess shares would otherwise have. Full voting power may be restored if a majority of the voting power of shares represented at a meeting, including those held by the party seeking restoration, are voted in favor of the restoration. This voting restriction does not apply to shares acquired directly from the corporation.

Sections 180.1140 to 180.1144 and 180.1150 of the WBCL do not currently apply to the Mayville Engineering Company, Inc. Employee Stock Ownership Plan, which we sometimes refer to as the ESOP, since they do not apply to the shares of our common stock currently held by our ESOP and our board of directors approved for purposes of these provisions any acquisition made by the ESOP after April 16, 2019.

Section 180.1134 of the WBCL requires shareholder approval for some transactions in the context of a tender offer or similar action for more than 5% of any class of a Wisconsin corporation's stock. Shareholder approval is required for the acquisition of more than 5% of the corporation's stock at a price above market value from any person who holds more than 3% of the voting shares and has held the shares for less than two years, unless the corporation makes an equal offer to acquire all shares. Shareholder approval is also required for the sale or option of assets that amount to at least 10% of the market value of the corporation, but this requirement does not apply if the corporation has at least three independent directors and a majority of the independent directors vote not to have this provision apply to the corporation.

Consideration of Constituencies

The WBCL allows directors and officers to consider constituencies other than shareholders, such as employees, suppliers, customers and the communities in which a corporation operates, in discharging their corporate duties.

In addition to the provisions described above, various provisions of our amended and restated articles and our bylaws, which are summarized in the following paragraphs, may be deemed to have anti-takeover effects.

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Staggered Board of Directors

Our articles and bylaws provide that the board of directors is divided into three classes, with staggered terms of three years each. Each year the term of one class expires. The articles provide that any vacancies on the board of directors can be filled only by the affirmative vote of a majority of the directors in office. Any director so elected will serve until the next election of the class for which he or she is chosen and until his or her successor is duly elected and qualified.

No Cumulative Voting

The WBCL provides that shareholders do not have the right to cumulate votes in the election of directors unless the articles of incorporation provide otherwise. Our articles do not provide for cumulative voting.

Meeting Procedures; Advance Notice Requirements for Shareholder Proposals and Director Nominations; Procedures for Calling a Special Meeting

Our bylaws provide the board of directors with discretion in postponing shareholder meetings, including, within certain limits, special meetings of shareholders. Additionally, the Chairman of the Board, the Chief Executive Officer or the President or the board of directors (acting by resolution) can adjourn a shareholder meeting at any time before business is transacted at the meeting.

Our bylaws also provide that shareholders seeking to bring business before an annual meeting must provide timely notice of their proposal in writing to the corporate secretary. To be timely, a shareholder's notice must have been received on or before December 31 of the year immediately preceding the annual meeting; provided, however, that in the event that the date of the annual meeting is on or after May 1 in any year, notice by the shareholder to be timely must be received not later than the close of business on the day which is determined by adding to December 31 of the year immediately preceding such annual meeting the number of days starting with May 1 and ending on the date of the annual meeting in such year. The bylaws also specify requirements as to the form and content of a shareholder's notice. These provisions may impede shareholders' ability to bring matters before an annual meeting of shareholders or make nominations for directors at an annual meeting of shareholders.

Our bylaws also establish a procedure which shareholders seeking to call a special meeting of shareholders must satisfy. This procedure involves notice to us, the receipt by us of written demands for a special meeting from holders of 10% or more of all the votes entitled to be cast on any issue proposed to be considered, a review of the validity of such demands by an independent inspector and the fixing of the record and meeting dates by the board of directors. In addition, shareholders demanding a special meeting must deliver a written agreement to pay the costs incurred by us in holding a special meeting, including the costs of preparing and mailing the notice of meeting and the proxy materials for the solicitation of proxies, in the event such shareholders are unsuccessful in their proxy solicitation.

Authorized But Unissued Shares

Our authorized but unissued shares of common stock and preferred stock are available for future issuance without shareholder approval. We could use these additional shares for a variety of corporate purposes, including future public offerings to raise additional capital, acquisitions of other businesses or entities and issuances under employee benefit plans. Additionally, we could issue a series of preferred stock that could, depending on its terms, impede the completion of a merger, tender offer or other takeover attempt. Our board of directors will make any determination to issue such shares based on its judgment as to the best interests of us and our shareholders. The board of directors, in so acting, could issue preferred stock having terms that could discourage an acquisition attempt through which an acquiror may be able to change the composition of the board of directors, including a tender offer or other transaction that some, or a majority, of our shareholders might believe to be in their best interests or in which shareholders might receive a premium over the then-current market price of the common stock.

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Supermajority Provisions

Our articles contain provisions that require the approval of 66 2/3% of the outstanding shares entitled to vote in order to amend certain anti-takeover provisions of the articles or bylaws. These provisions could have the effect of discouraging takeover attempts that some, or a majority, of our shareholders might believe to be in their best interests or in which shareholders might receive a premium over the then-current market price of our common stock.

Preemptive Rights

No holder of our common stock has any preemptive or subscription rights to acquire shares of our capital stock.

Amended and Restated Credit Agreement

Our Amended and Restated Credit Agreement contains a covenant that restricts our ability to permit any person or group other than the ESOP or the Mayville Engineering Company, Inc. 401(k) Plan to own or control more than 35% of our equity interests. In addition, the Amended and Restated Credit Agreement restricts our ability to permit our board of directors to not be composed of a majority of our continuing directors (i.e., our directors as of September 26, 2019 and any additional or replacement directors that have been approved by at least 51% of the directors then in office).

Liability and Indemnification of Officers and Directors

Pursuant to the WBCL and our bylaws, our directors and officers are entitled to mandatory indemnification against certain liabilities and expenses:

It should be noted that the WBCL specifically states that it is the public policy of Wisconsin to require or permit indemnification in connection with a proceeding involving securities regulation, as described therein, to the extent required or permitted as described above. Additionally, under the WBCL, our directors are not subject to personal liability to us, our shareholders or any person asserting rights on behalf thereof for certain breaches or failures to perform any duty resulting solely from their status as directors except in circumstances paralleling those in the final four bullet points above.

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DESCRIPTION OF THE DEBT SECURITIES

The following description of the terms of the debt securities sets forth the material terms and provisions of the debt securities to which any prospectus supplement may relate. The particular terms of any debt securities offered by any prospectus supplement and the extent, if any, to which the provisions described in this prospectus may apply to such offered debt securities will be described in the prospectus supplement relating to such offered debt securities. As used in this section, the terms "we," "us," "our," "MEC" and the "Company" refer to Mayville Engineering Company, Inc., a Wisconsin corporation, and not any of its subsidiaries, unless the context requires.

Senior debt securities will be issued under an indenture between us and a trustee named in the prospectus supplement, a form of which is filed as an exhibit to the registration statement of which this prospectus is a part. The indenture relating to the senior debt securities, as amended or otherwise supplemented by any supplemental indentures, is referred to in this prospectus as the indenture.

The following summaries of the material provisions of the indenture and the debt securities do not purport to be complete and are subject to, and are qualified in their entirety by reference to, all of the provisions of the indenture, including the definitions of specified terms used in the indenture, and the debt securities. Wherever particular articles, sections or defined terms of an indenture are referred to, it is intended that those articles, sections or defined terms will be incorporated herein by reference, and the statement in connection with which reference is made is qualified in its entirety by the article, section or defined term in the indenture.

General

The indenture does not limit the amount of debt securities that may be issued under the indenture, and the indenture does not limit the amount of other unsecured debt or securities that we may issue. The debt securities may be issued in one or more series with the same or various maturities and may be sold at par, a premium or an original issue discount. Some of the debt securities may be issued under the indenture as original issue discount securities to be sold at a substantial discount below their principal amount. Federal income tax and other considerations applicable to any original issue discount securities will be described in the related prospectus supplement. We have the right to "reopen" a previous issue of a series of debt by issuing additional debt securities of such series.

We conduct a substantial amount of our operations through subsidiaries and expect that we will continue to do so. Our right to participate as a shareholder in any distribution of assets of any subsidiary upon its liquidation or reorganization or otherwise and the ability of a holder of debt securities to benefit as our creditor from any distribution are subject to prior claims of creditors of the subsidiary. The debt securities will also effectively rank junior in right of payment to any of our secured debt.

The prospectus supplement relating to the particular series of debt securities offered thereby will describe the following terms of the offered debt securities:

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Payments

Unless otherwise indicated in any prospectus supplement, principal of and premium, if any, and interest, if any, on the offered debt securities will be payable, and transfers of the offered debt securities will be registrable, at the corporate trust office of the trustee. Alternatively, at our option, payment of interest may be made by check mailed to the address of the person entitled thereto as it appears in the debt security register.

Denominations, Registration and Transfer

Unless otherwise indicated in any prospectus supplement, the offered debt securities will be issued only in fully registered form without coupons in denominations of $1,000 or any integral multiple of $1,000, or the equivalent in foreign currency. Except as provided in the indenture, pursuant to a Board resolution, an officer's certificate or a supplemental indenture, no service charge will be made for any registration of transfer or exchange of offered debt securities or conversion or exchange of less than the entire principal amount of a debt security, but we may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection with any transfer or exchange.

If the purchase price of any of the offered debt securities is denominated in a foreign currency or currencies or if the principal of, premium, if any, or interest, if any, on any series of offered debt securities is payable in a foreign currency or currencies, the restrictions, elections, tax consequences, specific terms and other information with respect to the issue of offered debt securities and the foreign currency or currencies will be described in the related prospectus supplement.

We will not be required to issue, register the transfer of, or exchange debt securities of any series during the period from 15 days prior to the mailing of a notice of redemption of debt securities of that series to the date the notice is mailed. We will also not be required to register the transfer of or exchange any debt security so selected for redemption, except the unredeemed portion of any debt security being redeemed in part.

Conversion and Exchange

The terms, if any, on which debt securities of any series are convertible into or exchangeable for common stock or preferred stock, property or cash, or a combination of any of the foregoing, will be set forth in the related prospectus supplement. Terms may include provisions for conversion or exchange that is either mandatory, at the option of the holder, or at our option. The number of shares of common stock or preferred stock to be received by the holders of the debt securities will be calculated in the manner, according to the factors and at the time as described in the related prospectus supplement.

Merger

The indenture provides that we may, without the consent of the holders of debt securities, consolidate with, or sell, lease or convey all or substantially all of our assets to, or merge into any other corporation, provided that:

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In addition, we must provide to the trustee an opinion of legal counsel that any such transaction and any assumption by a successor corporation complies with the applicable provisions of the indenture and that we have complied with all conditions precedent provided in the indenture relating to such transaction.

Other than the covenants described above, or as set forth in any accompanying prospectus supplement, the indenture does not contain any covenants or other provisions designed to afford holders of the debt securities protection in the event of a takeover, recapitalization or a highly leveraged transaction involving us.

Modification of the Indenture

With the consent of the holders of more than 50% in aggregate principal amount of any series of debt securities then outstanding under the indenture, waivers, modifications and alterations of the terms of the indenture may be made which affect the rights of the holders of the series of debt securities. However, no modification or alteration may, without the consent of all holders of any series of debt securities then outstanding affected thereby:

In addition, as described in the description of "Events of Default" set forth below, holders of more than 50% in aggregate principal amount of the debt securities of any series then outstanding may waive past events of default in specified circumstances and may direct the trustee in enforcement of remedies.

We and the trustee may, without the consent of any holders, modify and supplement the indenture:

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Covenant Defeasance and Satisfaction and Discharge of a Series

Covenant Defeasance of any Series

If we deposit with the trustee, in trust, at or before maturity or redemption:

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in each case in an amount sufficient, after payment of all federal, state and local taxes in respect thereof payable by the trustee, in the opinion of a nationally-recognized firm of independent public accountants expressed in a written certification thereof delivered to the trustee, to pay when due the principal, premium, if any, and interest to maturity or to the redemption date, as the case may be, with respect to any series of debt securities then outstanding, and any mandatory sinking fund payments or similar payments or payment pursuant to any call for redemption applicable to such debt securities of such series on the day on which such payments are due and payable in accordance with the terms of the indenture and such debt securities, then the provisions of the indenture would no longer be effective as to the debt securities to which such deposit relates, including the restrictive covenants described in this prospectus or any prospectus supplement relating to such debt securities, except as to:

Defeasance of debt securities of any series is subject to the satisfaction of specified conditions, including, among others, the absence of an event of default at the date of the deposit and the perfection of the holders' security interest in the deposit.

Satisfaction and Discharge of any Series

Upon the deposit of money or securities contemplated above and the satisfaction of specified conditions, the provisions of the indenture (excluding the exceptions discussed above under the heading "Covenant Defeasance of any Series") would no longer be effective as to the related debt securities, we may cease to comply with our obligation to pay duly and punctually the principal of and premium, if any, and interest on a particular series of debt securities, the events of default in the indenture no longer would be effective as to such debt securities and thereafter the holders of the series of debt securities will be entitled only to payment out of the money or securities deposited with the trustee.

The specified conditions include, among others, except in limited circumstances involving a deposit made within one year of maturity or redemption:

Events of Default

As to any series of debt securities, an event of default is defined in the indenture as being:

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Notice and Declaration of Defaults

So long as the debt securities of any series remain outstanding, we will be required to furnish annually to the trustee a certificate of one of our corporate officers stating whether, to the best of such officer's knowledge, we are in default under any of the provisions of the indenture, and specifying all defaults, and the nature thereof, of which such officer has knowledge. We will also be required to furnish to the trustee copies of specified reports filed by us with the SEC.

The indenture provides that the trustee will, within 90 days after the occurrence of a default with respect to any series for which there are debt securities outstanding which is continuing, give to the holders of those debt securities notice of all uncured defaults known to it, including events specified above without grace periods. Except in the case of default in the payment of principal, premium, if any, or interest on any of the debt securities of any series or the payment of any sinking fund installment on the debt securities of any series, the trustee may withhold notice to the holders if the trustee in good faith determines that withholding notice is in the interest of the holders of the debt securities.

If a specified event of bankruptcy, insolvency, receivership, or reorganization occurs and is continuing, then the principal amount of (or, if the debt securities of that series are original issue discount debt securities, such portion of the principal amount as may be specified in their terms as due and payable upon acceleration) and any accrued and unpaid interest on that series will immediately become due and payable without any declaration or other act on the part of the trustee or any holder. If any other event of default occurs and is continuing, the trustee or the holders of not less than 25% in aggregate principal amount of the outstanding debt securities of any series may declare the debt securities of that series immediately due and payable. In some cases, the holders of a majority in principal amount of the debt securities of any series then outstanding may waive any past default and its consequences, except a default in the payment of principal, premium, if any, or interest, including sinking fund payments.

Actions upon Default

Subject to the provisions of the indenture relating to the duties of the trustee in case an event of default with respect to any series of debt securities occurs and is continuing, the indenture provides that the trustee will be under no obligation to exercise any of its rights or powers under the indenture at the request, order or direction of any of the holders of debt securities outstanding of any series unless the holders have offered to the trustee reasonable indemnity. The right of a holder to institute a proceeding with respect to the indenture is subject to conditions precedent including notice and indemnity to the trustee, but the holder has a right to receipt of principal, premium, if any, and interest on their due dates or to institute suit for the enforcement thereof, subject to specified limitations with respect to defaulted interest.

The holders of a majority in principal amount of the debt securities outstanding of the series in default will have the right to direct the time, method and place for conducting any proceeding for any remedy available to the trustee, or

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exercising any power or trust conferred on the trustee. Any direction by the holders will be in accordance with law and the provisions of the related indenture, provided that the trustee may decline to follow any such direction if the trustee determines on the advice of counsel that the proceeding may not be lawfully taken or would be materially or unjustly prejudicial to holders not joining in the direction. The trustee will be under no obligation to act in accordance with the direction unless the holders offer the trustee reasonable security or indemnity against costs, expenses and liabilities which may be incurred thereby.

Governing Law

The indenture and the debt securities will be governed by, and construed in accordance with, the laws of the State of New York.

Concerning the Trustee

We may from time to time maintain lines of credit, and have other customary banking relationships, with the trustee or its affiliates under the indenture.

The indenture and provisions of the Trust Indenture Act of 1939 that are incorporated by reference in the indenture contain limitations on the rights of the trustee, should it become one of our creditors, to obtain payment of claims in certain cases or to realize on certain property received by it in respect of any such claim as security or otherwise. The trustee is permitted to engage in other transactions with us or any of our affiliates. However, if it acquires any conflicting interest (as defined under the Trust Indenture Act of 1939), it must eliminate such conflict or resign.

Book-Entry, Delivery and Settlement

We may issue the debt securities in whole or in part in the form of one or more fully registered global securities that will be deposited with a depositary or its nominee identified in the applicable prospectus supplement and registered in the name of that depositary or nominee. In those cases, one or more registered global securities will be issued in a denomination or aggregate denominations equal to the portion of the aggregate principal or face amount of the debt securities to be represented by registered global securities. Unless and until it is exchanged in whole for debt securities in definitive registered form, a registered global security may not be transferred except as a whole by and among the depositary for the registered global security, the nominees of the depositary or any successors of the depositary or those nominees.

If not described below, any specific terms of the depositary arrangement with respect to any debt securities to be represented by a registered global security will be described in the prospectus supplement relating to those debt securities. We anticipate that the following provisions will apply to all depositary arrangements.

Ownership of beneficial interests in a registered global security will be limited to persons, called participants, that have accounts with the depositary or persons that may hold interests through participants. Upon the issuance of a registered global security, the depositary will credit, on its book-entry registration and transfer system, the participants' accounts with the respective principal or face amounts of the debt securities beneficially owned by the participants. Any dealers, underwriters or agents participating in the distribution of the debt securities will designate the accounts to be credited. Ownership of beneficial interests in a registered global security will be shown on, and the transfer of ownership interests will be effected only through, records maintained by the depositary, with respect to interests of participants, and on the records of participants, with respect to interests of persons holding through participants. The laws of some states may require that some purchasers of debt securities take physical delivery of these debt securities in definitive form. These laws may impair your ability to own, transfer or pledge beneficial interests in registered global securities.

So long as the depositary, or its nominee, is the registered owner of a registered global security, that depositary or its nominee, as the case may be, will be considered the sole owner or holder of the debt securities represented by the registered global security for all purposes under the Indenture. Except as described below, owners of beneficial interests in a registered global security will not be entitled to have the debt securities represented by the registered global security registered in their names, will not receive or be entitled to receive physical delivery of the debt securities in definitive

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form and will not be considered the owners or holders of the debt securities under the Indenture. Accordingly, each person owning a beneficial interest in a registered global security must rely on the procedures of the depositary for that registered global security and, if that person is not a participant, on the procedures of the participant through which the person owns its interest, to exercise any rights of a holder under the Indenture. We understand that under existing industry practices, if we request any action of holders or if an owner of a beneficial interest in a registered global security desires to give or take any action that a holder is entitled to give or take under the indenture, the depositary for the registered global security would authorize the participants holding the relevant beneficial interests to give or take that action, and the participants would authorize beneficial owners owning through them to give or take that action or would otherwise act upon the instructions of beneficial owners holding through them.

Principal, premium, if any, and interest payments on debt securities represented by a registered global security registered in the name of a depositary or its nominee will be made to the depositary or its nominee, as the case may be, as the registered owner of the registered global security. None of the Company, the Trustee, the security registrar or any other agent of the Company or agent of the Trustee or the security registrar will have any responsibility or liability for any aspect of the records relating to payments made on account of beneficial ownership interests in the registered global security or for maintaining, supervising or reviewing any records relating to those beneficial ownership interests.

We expect that the depositary for any of the debt securities represented by a registered global security, upon receipt of any payment of principal, premium, interest or other distribution of underlying securities or other property to holders on that registered global security, if any, will immediately credit participants' accounts in amounts proportionate to their respective beneficial interests in that registered global security as shown on the records of the depositary. We also expect that payments by participants to owners of beneficial interests in a registered global security held through participants will be governed by standing customer instructions and customary practices, as is now the case with the debt securities held for the accounts of customers or registered in "street name," and will be the responsibility of those participants.

If the depositary for any of these debt securities represented by a registered global security is at any time unwilling or unable to continue as depositary or ceases to be a clearing agency registered under the Exchange Act, and a successor depositary registered as a clearing agency under the Exchange Act is not appointed by us within 90 days, we will issue debt securities in definitive form in exchange for the registered global security that had been held by the depositary. Any debt securities issued in definitive form in exchange for a registered global security will be registered in the name or names that the depositary gives to the relevant security registrar or other relevant agent of ours or theirs. It is expected that the depositary's instructions will be based upon directions received by the depositary from participants with respect to ownership of beneficial interests in the registered global security that had been held by the depositary.

Euroclear and Clearstream

If the depositary for a global security is The Depository Trust Company, or "DTC," you may hold interests in the global security through Clearstream Banking, société anonyme, which we refer to as "Clearstream," or Euroclear Bank SA/NV, as operator of the Euroclear System, which we refer to as "Euroclear," in each case, as a participant in DTC. Euroclear and Clearstream will hold interests, in each case, on behalf of their participants through customers' securities accounts in the names of Euroclear and Clearstream on the books of their respective depositaries, which in turn will hold such interests in customers' securities in the depositaries' names on DTC's books.

Payments, deliveries, transfers, exchanges, notices and other matters relating to the debt securities made through Euroclear or Clearstream must comply with the rules and procedures of those systems. Those systems could change their rules and procedures at any time. We have no control over those systems or their participants, and we take no responsibility for their activities. Transactions between participants in Euroclear or Clearstream, on one hand, and other participants in DTC, on the other hand, would also be subject to DTC's rules and procedures.

Participants will be able to make and receive through Euroclear and Clearstream payments, deliveries, transfers, exchanges, notices and other transactions involving any debt securities held through those systems only on days when those systems are open for business. Those systems may not be open for business on days when banks, brokers and other institutions are open for business in the United States.

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In addition, because of time-zone differences, U.S. investors who hold their interests in the debt securities through these systems and wish on a particular day, to transfer their interests, or to receive or make a payment or delivery or exercise any other right with respect to their interests, may find that the transaction will not be effected until the next business day in Luxembourg or Brussels, as applicable. Thus, investors who wish to exercise rights that expire on a particular day may need to act before the expiration date. In addition, investors who hold their interests through both DTC and Euroclear or Clearstream may need to make special arrangements to finance any purchase or sales of their interests between the U.S. and European clearing systems, and those transactions may settle later than transactions within one clearing system.

DESCRIPTION OF WARRANTS

We may issue warrants for the purchase of debt securities, preferred stock, common stock or other securities. Warrants may be issued independently or together with debt securities, preferred stock or common stock offered by any prospectus supplement and may be attached to or separate from any such offered securities. Each series of warrants will be issued under a separate warrant agreement to be entered into between us and a bank or trust company, as warrant agent, all as will be set forth in the prospectus supplement relating to the particular issue of warrants. The warrant agent will act solely as our agent in connection with the warrants and will not assume any obligation or relationship of agency or trust for or with any holders of warrants or beneficial owners of warrants.

The following summary of certain provisions of the warrants does not purport to be complete and is subject to, and is qualified in its entirety by reference to, all provisions of the warrant agreements.

Reference is made to the prospectus supplement relating to the particular issue of warrants offered pursuant to such prospectus supplement for the terms of and information relating to such warrants, including, where applicable:

Warrants will be issued in registered form only. The exercise price for warrants will be subject to adjustment in accordance with provisions described in the applicable prospectus supplement.

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Each warrant will entitle the holder thereof to purchase such principal amount of debt securities or such number of shares of preferred stock, common stock or other securities at such exercise price as will in each case be set forth in, or calculable from, the prospectus supplement relating to the warrants, which exercise price may be subject to adjustment upon the occurrence of certain events as set forth in such prospectus supplement. After the close of business on the expiration date, or such later date to which such expiration date may be extended by us, unexercised warrants will become void. The place or places where, and the manner in which, warrants may be exercised will be specified in the prospectus supplement relating to such warrants.

Prior to the exercise of any warrants to purchase debt securities, preferred stock, common stock or other securities, holders of such warrants will not have any of the rights of holders of debt securities, preferred stock, common stock or other securities, as the case may be, purchasable upon such exercise, including the right to receive payments of principal of, premium, if any, or interest, if any, on the debt securities purchasable upon such exercise or to enforce covenants in the indenture, or to receive payments of dividends, if any, on the preferred stock, or common stock purchasable upon such exercise, or to exercise any applicable right to vote.

DESCRIPTION OF THE PURCHASE CONTRACTS AND PURCHASE UNITS

We may issue securities purchase contracts, including contracts obligating holders to purchase from us, and obligating us to sell to the holders, a specified number of shares of common stock or other securities at a future date or dates, which we refer to in this prospectus as "purchase contracts." The price per share of the securities and the number of shares of the securities may be fixed at the time the purchase contracts are issued or may be determined by reference to a specific formula set forth in the purchase contracts. The purchase contracts may be issued separately or as part of units consisting of a purchase contract and debt securities, preferred securities, warrants, other securities or debt obligations of third parties, including U.S. treasury securities, securing the holders' obligations to purchase the securities under the purchase contracts, which we refer to in this prospectus as "purchase units." The purchase contracts may require holders to secure their obligations under the purchase contracts in a specified manner. The purchase contracts also may require us to make periodic payments to the holders of the purchase units or vice versa, and those payments may be unsecured or refunded on some basis.

The purchase contracts, and, if applicable, collateral or depositary arrangements relating to the purchase contracts or purchase units, will be filed with the SEC in connection with the offering of purchase contracts or purchase units. The prospectus supplement relating to a particular issue of purchase contracts or purchase units will describe the terms of those purchase contracts or purchase units, including the following:

If we issue purchase units where debt obligations of third parties are used as security for your obligations to purchase or sell shares of common stock, preferred stock or other securities, we will include in the prospectus supplement relating to the offering information about the issuer of the debt securities. Specifically, if the issuer has a class of securities registered under the Exchange Act, and is either eligible to register its securities on Form S-3 under the Securities Act of 1933, as amended (the "Securities Act") or meets the listing criteria to be listed on a national securities exchange, we will include a brief description of the business of the issuer, the market price of its securities and how you can obtain more information about the issuer. If the issuer does not meet the criteria described in the previous sentence, we will include substantially all of the information that would be required if the issuer were making a public offering of the debt securities.

DESCRIPTION OF UNITS

We may issue units comprised of two or more of the securities described in this prospectus, in any combination, including, without limitation, the purchase units described above. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The units or the unit agreement or other agreement, if any, under which a unit is issued

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may provide that the securities included in the unit may not be held or transferred separately at any time, or at any time before a specified date.

The prospectus supplement relating to a particular issue of units will describe, among other things:

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports, proxy statements and other information with the SEC (File No. 001-38894). We also filed a registration statement on Form S-3, including exhibits, under the Securities Act with respect to the securities offered by this prospectus (Reg. No. 333-277747). This prospectus is a part of that registration statement, but does not contain all of the information included in the registration statement or the exhibits to the registration statement. The SEC maintains a website, www.sec.gov, that contains reports, proxy and information statements and other information regarding issuers that file electronically with the SEC. Our SEC filings are also available to the public on our website located at www.mecinc.com. However, we are not including the information contained on our website as part of, or incorporating it by reference into, this prospectus.

We are "incorporating by reference" specified documents that we file with the SEC, which means:

We incorporate by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this prospectus and before the end of the offering of the securities pursuant to this prospectus:

Notwithstanding the foregoing, information furnished under Items 2.02 and 7.01 of any Current Report on Form 8-K, including the related exhibits under Item 9.01, is not incorporated by reference.

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You may request a copy of any of these filings, at no cost, by request directed to us at the following address or telephone number:

Mayville Engineering Company, Inc.

135 South 84th Street, Suite 300

Milwaukee, Wisconsin 53214

(414) 381-2860

Attention: Secretary or General Counsel

You should not assume that the information in this prospectus and/or any prospectus supplement, as well as the information we file or previously filed with the SEC that we incorporate by reference in this prospectus and/or any prospectus supplement, is accurate as of any date other than its respective date. Our business, financial condition, results of operations and prospects may have changed since that date.

PLAN OF DISTRIBUTION

We may sell our securities in any one or more of the following ways from time to time: (i) through agents; (ii) to or through underwriters, including through underwriting syndicates represented by managing underwriters; (iii) through brokers or dealers; (iv) directly by us to purchasers, including through a specific bidding, auction or other process; or (v) through a combination of any of these methods of sale. Each time we offer and sell securities covered by this prospectus, we will make available a prospectus supplement or supplements that will describe the method of distribution and set forth the terms of the offering, including: (i) the name or names of any underwriters, dealers or agents and the amounts of securities underwritten or purchased by each of them; (ii) if a fixed price offering, the public offering price of the securities and the proceeds to us; (iii) any options under which underwriters may purchase additional securities from us; (iv) any underwriting discounts or commissions or agency fees and other items constituting underwriters' or agents' compensation; (v) terms and conditions of the offering; (vi) any discounts, commissions or concessions allowed or reallowed or paid to dealers; and (vii) any securities exchange or market on which the securities may be listed. Any dealers and agents participating in the distribution of the securities may be deemed to be underwriters, and compensation received by them on resale of the securities may be deemed to be underwriting discounts.

Any initial offering price, dealer purchase price, discount or commission may be changed from time to time.

The securities may be distributed from time to time in one or more transactions, at negotiated prices, at fixed prices (that may be subject to change), at market prices prevailing at the time of sale, at various prices determined at the time of sale or at prices related to prevailing market prices.

Offers to purchase securities may be solicited directly by us or by agents designated by us from time to time. Any such agent may be deemed to be an underwriter, as that term is defined in the Securities Act, of the securities so offered and sold.

If underwriters are utilized in the sale of any securities in respect of which this prospectus is being delivered, such securities will be acquired by the underwriters for their own account and may be resold from time to time in one or more transactions, including negotiated transactions, at fixed public offering prices or at varying prices determined by the underwriters at the time of sale. Securities may be offered to the public either through underwriting syndicates represented by managing underwriters or directly by one or more underwriters. If any underwriter or underwriters are utilized in the sale of securities, unless otherwise indicated in the applicable prospectus supplement, the obligations of the underwriters are subject to certain conditions precedent, and the underwriters will be obligated to purchase all such securities if any are purchased.

If a broker or dealer is utilized in the sale of the securities in respect of which this prospectus is delivered, we will sell such securities as principal. The broker or dealer may then resell such securities to the public at varying prices to be determined by such broker or dealer at the time of resale. Transactions through brokers or dealers may include block trades in which brokers or dealers will attempt to sell securities as agent but may position and resell as principal to

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facilitate the transaction or in cross trades, in which the same broker or dealer acts as agent on both sides of the trade. Any such broker or dealer may be deemed to be an underwriter, as such term is defined in the Securities Act, of the securities so offered and sold.

Offers to purchase securities may be solicited directly by us and the sale thereof may be made by us directly to institutional investors or others, who may be deemed to be underwriters within the meaning of the Securities Act with respect to any resale thereof.

If so indicated in the applicable prospectus supplement, we may authorize agents and underwriters to solicit offers by certain institutions to purchase securities from us at the public offering price set forth in the applicable prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on the date or dates stated in the applicable prospectus supplement. Such delayed delivery contracts will be subject only to those conditions set forth in the applicable prospectus supplement.

Agents, underwriters and dealers may be entitled under relevant agreements with us to indemnification by us against certain liabilities, including liabilities under the Securities Act, or to contribution with respect to payments that such agents, underwriters and dealers may be required to make in respect thereof. The terms and conditions of any indemnification or contribution will be described in the applicable prospectus supplement.

We may also sell shares of our common stock through various arrangements involving mandatorily or optionally exchangeable securities, and this prospectus may be delivered in connection with those sales.

We may enter into derivative, sale or forward sale transactions with third parties, or sell securities not covered by this prospectus to third parties in privately negotiated transactions. If the applicable prospectus supplement indicates, in connection with those transactions, the third parties may sell securities covered by this prospectus and the applicable prospectus supplement, including in short sale transactions and by issuing securities not covered by this prospectus but convertible into, or exchangeable for or representing beneficial interests in such securities covered by this prospectus, or the return of which is derived in whole or in part from the value of such securities. The third parties may use securities received under derivative, sale or forward sale transactions or securities pledged by us or borrowed from us or others to settle those sales or to close out any related open borrowings of stock, and may use securities received from us in settlement of those transactions to close out any related open borrowings of stock. The third party in such sale transactions will be an underwriter and will be identified in the applicable prospectus supplement (or a post-effective amendment).

Underwriters, brokers, dealers or agents may receive compensation in the form of commissions, discounts or concessions from us. Underwriters, brokers, dealers or agents may also receive compensation from the purchasers of securities for whom they act as agents or to whom they sell as principals, or both. Compensation as to a particular underwriter, broker, dealer or agent might be in excess of customary commissions and will be in amounts to be negotiated in connection with transactions. In effecting sales, brokers or dealers engaged by us may arrange for other brokers or dealers to participate in the resales.

Each series of securities offered, other than common stock, will be a new issue and, other than the common stock, which is listed on the New York Stock Exchange, will have no established trading market. We may elect to list any series of securities on an exchange, and in the case of the common stock, on any additional exchange, but, unless otherwise specified in the applicable prospectus supplement, we shall not be obligated to do so. No assurance can be given as to the liquidity of the trading market for any of the securities.

Agents, underwriters and dealers may engage in transactions with, or perform services for, us or our subsidiaries in the ordinary course of business.

Any underwriter may engage in overallotment, stabilizing transactions, short covering transactions and penalty bids in accordance with Regulation M under the Exchange Act. Overallotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Short covering transactions involve purchases of the securities in

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the open market after the distribution is completed to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time. An underwriter may carry out these transactions on a stock exchange, in the over-the-counter market or otherwise.

The place and time of delivery for securities will be set forth in the applicable prospectus supplement for such securities.

LEGAL MATTERS

The validity of the securities offered by this prospectus will be passed upon for us by Foley & Lardner LLP. The validity of the securities offered by this prospectus will be passed upon for any underwriters or agents by counsel named in the applicable prospectus supplement. The opinions of Foley & Lardner LLP and counsel for any underwriters or agents may be conditioned upon and may be subject to assumptions regarding future action required to be taken by us and any underwriters, dealers or agents in connection with the issuance of any securities. The opinions of Foley & Lardner LLP and counsel for any underwriters or agents may be subject to other conditions and assumptions, as indicated in the prospectus supplement.

EXPERTS

The financial statements of Mayville Engineering Company, Inc. incorporated by reference in this prospectus have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report. Such financial statements are incorporated by reference in reliance upon the report of such firm, given their authority as experts in accounting and auditing.

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Mayville Engineering Company, Inc.

4,348,000 Shares

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Common Stock

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PROSPECTUS SUPPLEMENT

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William Blair Craig-Hallum

Northland Capital Markets

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May 19, 2026

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