TETRA TECH INC

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of

the Securities Exchange Act of 1934 (Amendment No. )

Filed by the Registrant ☒

Filed by a Party other than the Registrant ☐

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Preliminary Proxy Statement

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Confidential, for Use of the Commission Only (as permitted by Rule 14a 6(e)(2))

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Definitive Proxy Statement

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Definitive Additional Materials

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Soliciting Material under §240.14a 12

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Tetra Tech, Inc.

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(Name of Registrant as Specified in Its Charter)

N/A

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(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

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No fee required.

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Fee paid previously with preliminary materials.

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Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a 6(i)(1) and 0-11.

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Today, Tetra Tech’s differentiated high-end consulting services are more in demand than ever before. With our focus on Leading with Science®, we are ideally positioned to provide the sustainable solutions that are needed in a changing world.

Dan Batrack

Chairman and Chief Executive Officer

January 2026

Dear Tetra Tech Stockholders:

You are cordially invited to attend the 2026 Annual Meeting of Stockholders of Tetra Tech, which will be held on Thursday, February 19, 2026, at 10:00 a.m. Pacific Time.

Details of the business to be conducted at the 2026 Annual Meeting are given in the accompanying Notice of 2026 Annual Meeting of Stockholders and the proxy statement.

We use the internet as our primary means of furnishing proxy materials to our stockholders. We will mail a Notice of Internet Availability of Proxy Materials to our stockholders of record that did not request to receive a printed copy of our proxy materials on or about January 9, 2026 with instructions for accessing the proxy materials and voting via the Internet. Consequently, most stockholders will not receive paper copies of our proxy materials and will instead receive a notice with instructions for accessing the proxy materials and voting via the internet. The notice also provides information on how stockholders can obtain paper copies of our proxy materials if they choose. Internet transmission and voting are designed to be efficient, minimize cost, and conserve natural resources.

Whether or not you plan to attend the 2026 Annual Meeting, please vote as soon as possible. As an alternative to voting in person at the 2026 Annual Meeting, you may vote via the internet, by telephone, or by mail. Voting by any of these methods will ensure your representation at the 2026 Annual Meeting.

Thank you for your continued support of Tetra Tech. We look forward to seeing you at the 2026 Annual Meeting.

Sincerely,

Dan Batrack

Chairman and Chief Executive Officer

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3475 E. Foothill Boulevard, Pasadena, California 91107

(626) 351-4664

tetratech.com​

Notice of 2026 Annual

Meeting of Stockholders

2026 Annual Meeting of Stockholders

Items of Business

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How to vote: Your vote is important

Dear Tetra Tech Stockholders:

Your vote is important. Even if you cannot attend the 2026 Annual Meeting, it is important that your shares be represented and voted. To ensure your representation at the 2026 Annual Meeting, you may submit your proxy and voting instructions via the internet, by telephone, or by mail by following the instructions listed on your proxy card, notice, or voting instruction form.

Please refer to “Voting Your Shares” in the Meeting and Voting Information section on page 80 of the accompanying proxy statement for a description of each voting method. If your shares are held by a bank, broker, or other nominee (your record holder) and you have not given your record holder instructions on how to vote your shares, your record holder will not be able to vote your shares on any matter other than ratification of the appointment of the independent registered public accounting firm. We strongly encourage you to vote.

On behalf of the Board of Directors, management, and employees of Tetra Tech, we thank you for your continued support.

By order of the Board of Directors,

Preston Hopson

Secretary

January 9, 2026

Pasadena, California

Important Notice about the Availability of Proxy Materials. The Notice of the 2026 Annual Meeting, proxy statement, and our 2025 Annual Report on Form 10-K are available at proxyvote.com. You are encouraged to access and review all the important information contained in our proxy materials before voting.