BANNER CORP

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

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☐ Preliminary proxy statement

☐ Confidential, for use of the Commission only (as permitted by Rule 14a-6(e)(2))

☒ Definitive proxy statement

☐ Definitive additional materials

☐ Soliciting material pursuant to § 240.14a-12

BANNER CORPORATION

(Name of registrant as specified in its charter)

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Proxy Statement

Dear

Shareholder:

You are cordially invited to attend the annual meeting of shareholders of Banner Corporation, which will be held on Thursday, May 22, 2025, at 10:00 a.m., Pacific Time. Our 2025 annual meeting of shareholders will be a virtual meeting conducted solely online via live webcast. There is no physical location for the annual meeting. The online meeting format will facilitate remote shareholder attendance and participation, including the ability to vote your shares electronically and submit questions during the meeting.

You can attend the meeting by visiting https://meetnow.global/MKLZ2QL. To participate in the annual meeting, registered shareholders will need the control number included on their proxy card and all other shareholders will need to follow the instructions that accompanied their proxy materials.

The Notice of Annual Meeting of Shareholders and Proxy Statement describe the formal business to be transacted at the meeting. Directors and officers of Banner Corporation, as well as a representative of Moss Adams LLP, our independent registered public accounting firm, will be available to respond to shareholder questions. We intend to answer questions pertinent to our business immediately following the formal meeting of shareholders.

It is important that your shares are represented at the meeting, whether or not you attend the meeting virtually and regardless of the number of shares you own. To make sure your shares are represented, we urge you to vote promptly. You may vote your shares via the Internet or a toll-free telephone number, or by completing and mailing your proxy card. If you attend the virtual meeting as a shareholder, you may vote your shares at that time even if you have previously submitted your proxy.

We hope you can attend the virtual annual meeting.

Sincerely,

Mark J. Grescovich

President and Chief Executive Officer

Notice of Annual Meeting of Shareholders

Items of Business

Proposal 1. Election of eleven directors to each serve for a one-year term.

Proposal 2. Advisory (non-binding) approval of the compensation of our named executive officers as disclosed in this Proxy Statement.

Proposal 3. Advisory (non-binding) approval on whether future advisory votesto approve executive compensation should be held every one, two or three years.

Proposal 4. Ratification of the Audit Committee’s appointment of Moss Adams LLP as our independent registered public accounting firm for 2025.

Proposal 5. Approval of the Adoption of the Banner Corporation 2025 Employee Stock Purchase Plan.

We will also consider and act upon such other matters as may properly come before the meeting or any adjournments or postponements thereof. As of the date of this notice, we are not aware of any other business to come before the annual meeting.

Your Vote is Important

To ensure your shares are represented at the meeting, please vote via the Internet or telephone, or sign, date and mail your proxy card which is solicited on behalf of the Board of Directors. The proxy will not be used if you attend and vote at the virtual annual meeting. Regardless of the number of shares you own, your vote is very important. Please act today.

Our 2025 annual meeting of shareholders will be a virtual meeting conducted solely online via live webcast. There is no physical location for the annual meeting. The online meeting format will facilitate remote shareholder attendance and participation, including the ability to vote your shares electronically and submit questions during the meeting. To participate in the annual meeting, registered shareholders will need the control number included on their proxy card and all other shareholders will need to follow the instructions that accompanied their proxy materials. A copy of the list of Banner shareholders on the record date will be available for inspection, via the “Shareholder” login on the virtual meeting website noted above, by any shareholder (or their agents or attorneys) beginning ten days prior to the meeting and continuing through the meeting. Beneficial owners of shares held in street name who wish to attend the meeting as a “Shareholder” must register with Computershare no later than 5:00 p.m., Eastern Time, on May 16, 2025. (Late submissions may be processed to the extent feasible, but registration cannot be guaranteed in time for participation in the meeting.) To request registration, forward the proxy-granting email from your broker or email an image of your legal proxy tolegalproxy@computershare.com, with a subject line of “Legal Proxy,” or mail your request to Computershare, Banner Corporation Legal Proxy, P.O. Box 43006, Providence, RI 02940-3006. Computershare will confirm your registration and provide you with a unique control number necessary to participate fully in the meeting.

BY ORDER OF THE BOARD OF DIRECTORS

SHERREY LUETJEN

Secretary, Banner Corporation

Walla Walla, Washington

IMPORTANT: Voting promptly will save us the expense of further requests for proxies in order to ensure a quorum. You may vote via the Internet or by telephone or by submitting your proxy card by mail.