Exhibit 99.1

NEWS RELEASE January 28, 2026

Tetra Tech Reports Strong First Quarter 2026 Results and

Raises Fiscal Year 2026 Guidance

Pasadena, California. Tetra Tech, Inc. (NASDAQ: TTEK), a leading provider of high-end consulting and engineering services in water, environment and sustainable infrastructure, today announced results for the first quarter ended December 28, 2025.

Revenue and revenue, net of subcontractor costs (net revenue)1, in the first quarter totaled $1.21 billion and $1.04 billion, respectively. Operating income was $141 million and adjusted EBITDA1 was $147 million; adjusted EBITDA margin up 140 basis points year-over-year. EPS was $0.40 and adjusted EPS1 was $0.35. Backlog was $3.95 billion at the end of the first quarter. Cash from operations was $72 million in the first quarter and $517 million over the trailing 12 months.

Q1 FY26 Highlights (Excluding USAID / DOS)

Executive Management Comments

Dan Batrack, Chairman and CEO, commented, “Tetra Tech began fiscal 2026 with a strong first quarter as net revenue was up 8% and EPS up 17%. Subsequent to the first quarter, we announced two strategic acquisitions, further expanding our front-end consulting business for our defense clients. As expected, our margin increased by 80 basis points, with our higher margin front-end advisory and technical consulting business growing at a double-digit rate. With the promotion of Roger Argus to CEO effective after our annual shareholders meeting, I see continued progress toward achieving our 2030 vision and direction and the associated financial targets.”

Roger Argus, President and CEO-designate, stated, “We continued to see significant demand for our differentiated services in water, environment, and sustainable infrastructure across our global operations. During the quarter, we grew our government business with municipal water and defense clients, and on the commercial side, we saw an increase in power and transmission projects to support energy demand. As a result, we are increasing our guidance for 2026 and are well positioned to achieve our 2030 goals.”

Quarterly Dividend and Share Repurchase Program

On January 26, 2026, Tetra Tech’s Board of Directors approved the Company’s 47th consecutive quarterly dividend at an amount of $0.065 per share, a 12% increase year-over-year, payable on February 27, 2026, to stockholders of record as of February 12, 2026. In the first quarter, Tetra Tech repurchased $50 million of common stock. Additionally, as of December 28, 2025, the Company had $548 million remaining under its share repurchase programs.

Business Outlook

The following statements are based on current expectations. These statements are forward-looking, and the actual results could differ materially. These statements do not include the potential impact of transactions that may be completed or developments that become evident after the date of this release. The Business Outlook section should be read in conjunction with the information on forward-looking statements at the end of this release.

For fiscal 2026, Tetra Tech is increasing the full year guidance for net revenue2 to range from $4.15 billion to $4.30 billion and adjusted EPS3 to range from $1.46 to $1.56. For the second quarter of fiscal 2026, Tetra Tech expects net revenue to range from $975 million to $1.025 billion and EPS to range from $0.30 to $0.33.

Webcast

Investors will have the opportunity to access a live audio-visual webcast and supplemental financial information concerning the first quarter of fiscal 2026 results through a link posted on the Company’s website at tetratech.com on January 29, 2026, at 8:00 a.m. (PT).

Reconciliation of GAAP and Non-GAAP Items

In thousands (except EPS data)

About Tetra Tech

Tetra Tech is the leader in water, environment and sustainable infrastructure, providing high-end consulting and engineering services for projects worldwide. With more than 25,000 employees working together, Tetra Tech provides clear solutions to complex problems by Leading with Science® to address the entire water cycle, protect and restore the environment, and design sustainable and resilient infrastructure. For more information about Tetra Tech, please visit tetratech.com or follow us on LinkedIn and Facebook.

CONTACTS:
Jim Wu, Investor Relations
Charlie MacPherson, Media & Public Relations
(626) 470-2844

Forward-Looking Statements

This release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. The use of words such as "anticipate," "expect," "could," "may," "intend," "plan" and "believe," among others, generally identify forward-looking statements. These forward-looking statements are based on current expectations and beliefs of Tetra Tech’s management and currently available operating, financial, economic and other information, and are subject to a number of risks and uncertainties. Readers are cautioned that these forward-looking statements are only predictions and may differ materially from actual future events or results. A variety of factors, many of which are beyond our control, could cause actual future results or events to differ materially from those projected in the forward-looking statements in this release, including but not limited to: continuing worldwide political and economic uncertainties; the U.S. Administration’s potential changes to fiscal policies; the cyclicality in demand for our overall services; the fluctuation in demand for oil and gas, and mining services; risks related to international operations; concentration of revenues from U.S. government agencies and potential funding disruptions by these agencies; dependence on winning or renewing U.S. government contracts; the delay or unavailability of public funding on U.S. government contracts; the U.S. government’s right to modify, delay, curtail or terminate contracts at its convenience; compliance with government procurement laws and regulations; the impact of global pandemics; credit risks associated with certain clients in certain geographic areas or industries; acquisition strategy and integration risks; goodwill or other intangible asset impairment; the failure to comply with worldwide anti-bribery laws; the failure to comply with domestic and international export laws; the failure to properly manage projects; the loss of key personnel or the inability to attract and retain qualified personnel; the ability of our employees to obtain government granted eligibility; the use of estimates and assumptions in the preparation of financial statements; the ability to maintain adequate workforce utilization; the use of the percentage-of-completion method of accounting; the inability to accurately estimate and control contract costs; the failure to adequately recover on our claims for additional contract costs; the failure to win or renew contracts with private and public sector clients; growth strategy management; backlog cancellation and adjustments; risks relating to cyber security breaches; the failure of partners to perform on joint projects; the failure of subcontractors to satisfy their obligations; requirements to pay liquidated damages based on contract performance; the adoption of new legal requirements; changes in resource management, environmental or infrastructure industry laws, regulations or programs; changes in bank and capital markets and the access to capital; credit agreement covenants; industry competition; liability related to legal proceedings, investigations, and disputes; the availability of third-party insurance coverage; the ability to obtain adequate bonding; employee, agent, or partner misconduct; employee risks related to international travel; safety programs; conflict of interest issues; liabilities relating to reports and opinions; liabilities relating to environmental laws and regulations; force majeure events; protection of intellectual property rights; stock price volatility; the ability to impede a business combination based on Delaware law and charter documents; and other risks and uncertainties as may be described in Tetra Tech’s periodic filings with the Securities and Exchange Commission, including those described in the “Risk Factors” section of Tetra Tech’s Annual Report on Form 10-K for the fiscal year ended September 28, 2025. Readers should not place undue reliance on forward-looking statements since such information speaks only as of the date of this release. Tetra Tech does not intend to update forward-looking statements and expressly disclaims any obligation to do so.

Non-GAAP Financial Measures

To supplement the financial results presented in accordance with generally accepted accounting principles in the United States (“GAAP”), we present certain non-GAAP financial measures within the meaning of Regulation G under the Securities Exchange Act of 1934, as amended. We provide these non-GAAP financial measures because we believe they provide a valuable perspective on our financial results. However, non-GAAP measures have limitations as analytical tools and should not be considered in isolation and are not in accordance with, or a substitute for, GAAP measures. In addition, other companies may define non-GAAP measures differently which limits the ability of investors to compare non-GAAP measures of Tetra Tech to those used by our peer companies. A reconciliation of these non-GAAP financial measures to the most directly comparable GAAP financial measures is set forth above in this release.

Tetra Tech, Inc.

Balance Sheet - Unaudited

(unaudited - in thousands, except par value)

Tetra Tech, Inc.

Consolidated Statements of Income

(unaudited - in thousands, except per share data)

Tetra Tech, Inc.

Consolidated Statements of Cash Flows

(unaudited - in thousands)

Tetra Tech, Inc.

Regulation G Information

December 28, 2025

Reconciliation of Revenue to Revenue, Net of Subcontractor Costs ("Net Revenue")

(in millions)

Reconciliation of Net Income Attributable to Tetra Tech to Adjusted EBITDA

(in thousands)

1 Includes write-off of deferred debt origination fees of $3.8M in fiscal 2023

2 Includes lease impairment charge of $16.4M in fiscal 2023