Otter Tail Corp

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

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OTTER TAIL CORPORATION

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OTTER TAIL CORPORATION

ANNUAL MEETING OF SHAREHOLDERS

Monday, April 13, 2026

10:00 A.M. (CDT)

Virtual Meeting Link: www.virtualshareholdermeeting.com/OTTR2026.

In order to be admitted to the Annual Meeting, you will need to enter the 16-Digit Control Number found on your proxy card, voting instruction form, or Notice you previously received. You may vote during the Annual Meeting by following the instructions that will be available on the virtual meeting website.

Contact Shareholder

Services for Information

March 2, 2026

Dear Shareholders:

Otter Tail Corporation produced strong financial results in 2025, showcasing our team members’ hard work and commitment to our mission - delivering value through building strong electric and manufacturing platforms for our shareholders, customers and employees. We generated diluted earnings per share of $6.55, and ended the year in a position of financial strength, with a balance sheet capable of funding our customer-focused growth plan without any near-term external equity needs. We produced a utility sector leading return on equity of 16 percent on an equity layer of 63 percent.

For the fifth year in a row, we received the Edison Electric Institute (EEI) Index Award for the top performing small-capitalization utility with a total shareholder return of 158 percent over the five-year period ending September 30, 2025. Our five-year total shareholder return for the period ending September 30, 2025 was the highest of all EEI member companies.

Earlier this year, we increased our dividend by 10 percent, producing an annual indicated dividend of $2.31 per share. This is the second year in a row we have announced a double-digit increase to our dividend, reflecting our commitment to delivering shareholder value and returning money to shareholders. 2026 will mark the 88th consecutive year Otter Tail Corporation has paid dividends to our shareholders without reduction or interruption.

In 2025, our regulated electric utility, Otter Tail Power Company, continued to deliver on our significant rate base growth plan. We made progress on a number of capital projects, including our wind repowering project, two solar development projects and our large regional transmission projects.

Our manufacturing businesses focused on aligning our cost structure with the softened demand environment while ensuring we remained well positioned to respond when conditions improve. We completed our BTD Georgia expansion project in early 2025 and look forward to better serving our growing customers located in the southeastern part of the U.S.

Our PVC pipe businesses produced earnings that outpaced our original expectations for the year despite our sales prices of PVC pipe continuing to recede from peak levels. Throughout 2025, we benefitted from the production capacity added at our Vinyltech facility in late 2024 with higher sales volumes.

Our governance and executive compensation practices reinforce our accountability to our shareholders. Independent board oversight of management, stock ownership requirements for directors and officers and compensation programs designed for performance based pay align our interests with those of our shareholders.

We invite you to join us at our virtual 2026 Annual Meeting of Shareholders on Monday, April 13, 2026 at 10:00 a.m. (CDT), and look forward to providing you with more details about our 2025 operational and financial results, as well as our customer-focused growth strategy during the meeting.

Your vote is important. Information concerning the matters to be considered and voted upon at the 2026 Annual Meeting along with instructions on how to vote your shares is set out in the attached Notice of 2026 Annual Meeting and Proxy Statement.

Thank you for your confidence and investment in Otter Tail Corporation.

Charles MacFarlane, President and CEO, and Nathan Partain, Chairman of the Board

Notice of Annual Meeting

Table of Contents

Forward-Looking Statements

The statements contained in this Proxy Statement about our future performance and operations, including, without limitation, financial and operational results, use of renewable resources and carbon emissions reductions, strategies, visions, prospects, plans, targets, goals, objectives, opportunities, consequences and all other statements that are not purely historical, are forward-looking statements for purposes of the safe harbor provisions under The Private Securities Litigation Reform Act of 1995. Although we believe that our expectations are based on information currently available and on reasonable assumptions, we can give no assurance they will be achieved. There are a number of risks and uncertainties that could cause actual results to differ materially from any forward-looking statements made herein. A discussion of some of these risks and uncertainties is contained in our Annual Report on Form 10-K and subsequent reports filed with the Securities and Exchange Commission (“SEC”), and available on our website: www.ottertail.com. In addition, any forward-looking statements included herein represent our estimates only as of the date hereof and should not be relied upon as representing our estimates as of any subsequent date. While we may elect to update forward-looking statements from time to time, we specifically disclaim any obligation to do so, even if our internal estimates change, unless otherwise required by applicable securities laws.