Material Agreement (Form 8-K)

On July 21, 2025, Simmons First National Corporation (the "Company") entered into an underwriting agreement (the "Underwriting Agreement") with Stephens Inc., Keefe, Bruyette & Woods, Inc. and Morgan Stanley & Co. LLC as representatives of the several underwriters named in Schedule A thereto (the "Underwriters"), pursuant to which the Company agreed to issue and sell 18,653,000 shares of the Company's Class A common stock, par value $0.01 per share (the "Common Stock"), to the Underwriters (the "Offering") (including 2,433,000 shares pursuant to the Underwriters' option to purchase additional shares of Common Stock in the Offering (the "Option Shares")). The public offering price of shares of Common Stock sold in the Offering is $18.50 per share, and the Underwriters have agreed to purchase the shares from the Company pursuant to the Underwriting Agreement at a price of $17.575 per share. The Offering closed on July 23, 2025.

The net proceeds to the Company from the Offering, including the exercise by the Underwriter of its 30-dayoption to purchase any of the Option Shares, are expected to be approximately $326.9 million after deducting the underwriting discounts and commissions and estimated offering expenses payable by the Company. The Company intends to use the proceeds from the Offering for general corporate purposes, which may include investments in Simmons Bank to support a potential balance sheet repositioning and continued growth.

The Offering was made pursuant to the Company's Registration Statement on Form S-3ASR(File No. 333-279502),which was previously filed with the Securities and Exchange Commission and automatically effective as of May 17, 2024, as supplemented by a prospectus supplement, dated July 21, 2025.

The Underwriting Agreement contains customary representations, warranties and covenants of the Company and also provides for customary indemnification obligations of the Company and the Underwriters, including for liabilities under the Securities Act of 1933, as amended. The representations, warranties and covenants contained in the Underwriting Agreement were made only for purposes of such agreement and as of specific dates and were solely for the benefit of the parties to such agreement. The foregoing summary of the Underwriting Agreement is qualified in its entirety by reference to the Underwriting Agreement, a copy of which is filed as Exhibit 1.1 to this Current Report on Form 8-Kand 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 Common Stock 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.