Material Agreement, Financial Obligation (Form 8-K)

On September 12, 2025, Simmons First National Corporation (the "Company") completed its previously-announced public offering (the "Offering") of $325,000,000 aggregate principal amount of its 6.25% Fixed-to-FloatingRate Subordinated Notes due 2035 (the "Notes"). The Notes were offered and sold pursuant to the Company's registration statement on Form S-3ASR(Registration No. 333-279502)which was previously filed with the U.S. Securities and Exchange Commission (the "Commission") and automatically effective as of May 17, 2024, as supplemented by a preliminary prospectus supplement, filed with the Commission on September 9, 2025, and a final prospectus supplement, filed with the Commission on September 10, 2025. The Notes were issued pursuant to the Subordinated Indenture, dated as of March 26, 2018 (the "Base Indenture"), between the Company and Wilmington Trust, National Association (the "Trustee"), as supplemented by the Second Supplemental Indenture dated as of September 12, 2025 (the "Supplemental Indenture" and, together with the Base Indenture, the "Indenture"), between the Company and the Trustee.

The Notes are intended to qualify as Tier 2 capital for regulatory purposes. The net proceeds from the Offering were approximately $321.3 million, after deducting the underwriting discounts and commissions and estimated offering expenses payable by the Company. The Company intends to use the net proceeds from the Offering, together with cash on hand, to repay in full the Company's outstanding $330 million principal aggregate amount of the Floating-to-FixedRate Subordinated Notes due 2028 (the "2028 Notes"), on October 1, 2025, and for general corporate purposes.

The Notes sold in the Offering shall, from and including the date of original issuance to, but excluding, October 1, 2030, or the date of earlier redemption (the "fixed rate period"), bear interest at an initial rate of 6.25% per annum, payable semi-annually in arrears on April 1 and October 1 of each year, commencing on April 1, 2026. The last interest payment date for the fixed rate period will be October 1, 2030. From and including October 1, 2030 to, but excluding, October 1, 2035, or the date of earlier redemption (the "floating rate period"), the Notes will bear interest at a floating rate per annum equal to the Benchmark rate, which is expected to be Three-Month Term SOFR (each as defined in the Notes), plus a spread of 302 basis points for each quarterly interest period during the floating rate period, payable quarterly in arrears on January 1, April 1, July 1 and October 1 of each year, commencing on January 1, 2031. Notwithstanding the foregoing, if the Benchmark rate is less than zero, the Benchmark rate shall be deemed to be zero.

The Company may, at its option, redeem the Notes in whole or in part beginning with the interest payment date of October 1, 2030, and on any interest payment date thereafter. The Company may also redeem the Notes, in whole but not in part, upon the occurrence of certain specified events at the redemption prices provided therein, plus accrued and unpaid interest on the notes to, but excluding the redemption date. Any early redemption of the Notes will be subject to receipt of the approval of the Board of Governors of the Federal Reserve System to the extent required under applicable laws or regulations, including capital regulations. The Notes will not have the benefit of any sinking fund. The Notes are not obligations of, and are not, and will not be, guaranteed by any of the Company's subsidiaries.

The Notes are unsecured, subordinated obligations of the Company and (i) rank junior in right of payment to all of the Company's existing and future Senior Indebtedness (as defined in the Indenture); (ii) rank junior in right of payment to any of the Company's future general creditors; (iii) rank equal in right of payment with any of the Company's existing and future subordinated indebtedness, including the Company's outstanding 2028 Notes; (iv) rank senior in right of payment to any of the Company's future indebtedness the terms of which provide that such indebtedness ranks junior in right of payment of the Notes; and (v) are structurally subordinated to all of the Company's existing and future indebtedness, deposits and other liabilities of the Company's current and future subsidiaries, including without limitation, Simmons Bank's liabilities to depositors in connection with the deposits as well as liabilities to general creditors and liabilities arising in the ordinary course of business or otherwise.

The Indenture provides that the maturity of the Notes may only be accelerated upon the occurrence of certain events related to the bankruptcy or insolvency of the Company, whether voluntary or involuntary, or certain events related to the insolvency of Simmons Bank. There is no right of acceleration of the payment of principal of the Notes upon a default in the payment of principal of or interest on the Notes or in the performance of any of the Company's covenants or agreements contained in the Notes, in the Indenture or any of the Company's other obligations or liabilities.

The foregoing descriptions of the Base Indenture and the Supplemental Indenture do not purport to be complete and are qualified in their entirety by reference to the full text of such documents. For a complete description of the Base Indenture and the Supplemental Indenture, which includes the form of the Notes, please refer to the Base Indenture, attached as Exhibit 4.1 and the Supplemental Indenture, attached as Exhibit 4.2 to this Current Report on Form 8-K,which are incorporated herein by reference. The form of the Notes is included in Exhibit 4.3 and is incorporated herein by reference.

Troutman Pepper Locke LLP, counsel to the Company, delivered an opinion as to legality of the issuance and sale of the Notes in the Offering, a copy of which is filed as Exhibit 5.1 to this Current Report on Form 8-Kand incorporated herein by reference.

The information set forth above under Item 1.01 of this Current Report on Form 8-Kis incorporated by reference into this Item 2.03.