EXHIBIT 99.1 Exhibit 99.1 NEWS RELEASE January 28, 2026 Tetra Tech Reports Strong First Quarter 2026 Results and Raises Fiscal Year 2026 Guidance · Revenue $1.21 billion; Net Revenue $1.04 billion · Net Revenue up 8% excluding USAID/DOS and Q1-25 Hurricanes · Operating Income $141 million; Adjusted EBITDA $147 million · EPS $0.40; Adjusted EPS $0.35 · Raising FY26 Net Revenue and EPS 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 EBITDA 1 was $147 million; adjusted EBITDA margin up 140 basis points year-over-year. EPS was $0.40 and adjusted EPS 1 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) · Adjusted EBITDA margin improved 80 basis points year-over-year · EPS up 17% year-over-year · DSO improved to 51 days · Halvik acquisition expands high-end data analytics and resilient infrastructure optimization · Providence acquisition further advances front-end program advisory services · $151 billion ten-year multiple award contract for the U.S. Missile Defense Agency SHIELD program · $500 million multiple-award contract for environmental services for USACE Baltimore District · A$88 million single-award contract for coastal infrastructure planning services for Australia Defense · $60 million multiple-award contract for waterway design services for USACE Portland District · A$57 million single-award contract for naval facility resilience for Australia Defense 1 Non-GAAP financial measures which the Company believes provide valuable perspectives on its business results. Refer to tables at the end of the release and Regulation G Information for reconciliations to the comparable GAAP metrics. 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 47 th 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 revenue 2 to range from $4.15 billion to $4.30 billion and adjusted EPS 3 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). 2 Reconciliation of the net revenue guidance to the most directly comparable GAAP measure is not available without unreasonable efforts because the Company cannot predict the magnitude and timing of all the components, including subcontractor costs, required to provide such reconciliation with sufficient precision. 3 The only adjustments in our guidance for EPS are to exclude the gain on business disposition and contingent consideration in the first quarter of fiscal 2026. Reconciliation of GAAP and Non-GAAP Items In thousands (except EPS data) Three Months Ended December 28, 2025 December 29, 2024 Revenue $ 1,210,663 $ 1,420,561 USAID/DOS (56,374 ) (283,905 ) Revenue excl. USAID/DOS $ 1,154,289 $ 1,136,656 Revenue $ 1,210,663 $ 1,420,561 Subcontractor costs (173,487 ) (223,231 ) Net revenue $ 1,037,176 $ 1,197,330 USAID/DOS (50,606 ) (238,517 ) Net revenue excl. USAID/DOS $ 986,570 $ 958,813 Operating Income $ 140,994 $ 22,526 Contingent consideration (7,447 ) (366 ) Legal contingency - 115,000 Adjusted Operating Income $ 133,547 $ 137,160 USAID/DOS (2,746 ) (19,987 ) Adjusted OI excl. USAID/DOS $ 130,801 $ 117,173 EPS $ 0.40 $ 0.00 Contingent consideration (0.02 ) - Gain on business disposition (0.03 ) - Legal contingency - 0.35 Adjusted EPS $ 0.35 $ 0.35 USAID/DOS (0.01 ) (0.06 ) Adjusted EPS excl. USAID/DOS $ 0.34 $ 0.29 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) December 28, September 28, 2025 2025 Assets Current assets: Cash and cash equivalents 269,448 167,459 Accounts receivable, net 1,082,417 1,158,928 Contract assets 140,429 138,232 Prepaid expenses and other current assets 112,145 98,768 Assets held-for-sale - 57,502 Total current assets 1,604,439 1,620,889 Property and equipment, net 65,395 66,148 Right-of-use assets, operating leases 199,552 197,618 Goodwill 2,065,914 2,049,874 Intangible assets, net 113,567 121,160 Deferred tax assets 92,638 106,238 Other non-current assets 123,222 120,247 Total assets 4,264,727 4,282,174 Liabilities and Equity Current liabilities: Accounts payable 196,730 204,725 Accrued compensation 221,817 346,912 Contract liabilities 435,373 420,254 Short-term lease liabilities, operating leases 69,681 69,099 Current contingent earn-out liabilities 18,093 24,826 Liabilities held-for-sale - 25,115 Other current liabilities 279,100 288,113 Total current liabilities 1,220,794 1,379,044 Deferred tax liabilities 20,171 21,333 Long-term debt 834,256 763,363 Long-term lease liabilities, operating leases 154,444 154,695 Non-current contingent earn-out liabilities 33,299 32,135 Other non-current liabilities 155,125 151,440 Total liabilities 2,418,089 2,502,010 Equity: Preferred stock - authorized, 2,000 shares of $0.01 par value; no shares issued and outstanding at December 28, 2025 and September 28, 2025 - - Common stock - authorized, 750,000 shares of $0.01 par value; issued and outstanding, 260,811 and 261,418 shares at December 28, 2025 and September 28, 2025, respectively 2,608 2,614 Accumulated other comprehensive loss (76,356 ) (95,777 ) Retained earnings 1,919,840 1,872,948 Tetra Tech stockholders' equity 1,846,092 1,779,785 Noncontrolling interests 546 379 Total stockholders' equity 1,846,638 1,780,164 Total liabilities and stockholders' equity 4,264,727 4,282,174 Tetra Tech, Inc. Consolidated Statements of Income (unaudited - in thousands, except per share data) Three Months Ended December 28, December 29, 2025 2024 Revenue $ 1,210,663 $ 1,420,561 Subcontractor costs (173,487 ) (223,231 ) Other costs of revenue (816,805 ) (975,853 ) Gross profit 220,371 221,477 Selling, general and administrative expenses (86,824 ) (84,317 ) Legal contingency costs - (115,000 ) Contingent consideration - fair value adjustments 7,447 366 Income from operations 140,994 22,526 Interest expense, net (7,128 ) (7,218 ) Other non-operating income 7,710 - Income before income tax expense 141,576 15,308 Income tax expense (36,354 ) (14,530 ) Net income 105,222 778 Net income attributable to noncontrolling interests (194 ) (31 ) Net income attributable to Tetra Tech $ 105,028 $ 747 Earnings per share attributable to Tetra Tech: Basic $ 0.40 $ - Diluted $ 0.40 $ - Weighted-average common shares outstanding: Basic 260,809 267,854 Diluted 262,731 271,886 Tetra Tech, Inc. Consolidated Statements of Cash Flows (unaudited - in thousands) Three Months Ended December 28, December 29, 2025 2024 Cash flows from operating activities: Net income $ 105,222 $ 778 Adjustments to reconcile net income to net cash provided by operating activities: Depreciation and amortization 13,996 16,063 Amortization of stock-based awards 8,182 8,142 Deferred income taxes 13,085 767 Provision for losses on accounts receivables 960 - Gain on sale of divested business (7,710 ) - Fair value adjustments to contingent consideration (7,447 ) (366 ) Other non-cash items 861 1,141 Changes in operating assets and liabilities, net of effects of divestiture: Accounts receivable and contract assets 79,945 (91,725 ) Prepaid expenses and other assets (17,927 ) (26,186 ) Accounts payable (8,824 ) 44,194 Accrued compensation (126,658 ) (101,641 ) Contract liabilities 13,213 27,527 Income taxes receivable/payable 2,450 (1,538 ) Cash settled contingent earn-out liability - (2,720 ) Other liabilities 2,919 138,627 Net cash provided by operating activities 72,267 13,063 Cash flows from investing activities: Capital expenditures (4,152 ) (3,433 ) Proceeds from divested business, net 41,612 - Net cash provided by (used in) investing activities 37,460 (3,433 ) Cash flows from financing activities: Proceeds from borrowings 70,000 90,000 Repayments on long-term debt - (15,000 ) Repurchases of common stock (50,000 ) (25,000 ) Shares repurchased for tax withholdings on share-based awards (11,864 ) (13,307 ) Payments of contingent earn-out liabilities - (145 ) Stock options exercised 10 114 Dividends paid (16,937 ) (15,549 ) Principal payments on finance leases (2,083 ) (1,719 ) Net cash provided by (used in) financing activities (10,874 ) 19,394 Effect of exchange rate changes on cash and cash equivalents 2,223 (13,609 ) Net increase in cash and cash equivalents 101,076 15,415 Cash and cash equivalents at beginning of period 168,372 232,689 Cash and cash equivalents at end of period $ 269,448 $ 248,104 Tetra Tech, Inc. Regulation G Information December 28, 2025 Reconciliation of Revenue to Revenue, Net of Subcontractor Costs ("Net Revenue") (in millions) 2025 2026 2023 2024 1st Qtr 2nd Qtr 6 Mos 3rd Qtr 9 Mos 4th Qtr Full Year 1st Qtr Consolidated Revenue 4,522.6 5,198.7 1,420.6 1,322.1 2,742.7 1,369.8 4,112.5 1,330.1 5,442.6 1,210.7 Subcontractor Costs (771.5 ) (876.8 ) (223.3 ) (218.4 ) (441.7 ) (216.8 ) (658.5 ) (166.8 ) (825.3 ) (173.5 ) Net Revenue 3,751.1 4,321.9 1,197.3 1,103.7 2,301.0 1,153.0 3,454.0 1,163.3 4,617.3 1,037.2 GSG Segment Revenue 2,300.7 2,624.2 791.4 698.9 1,490.2 709.4 2,199.6 628.9 2,828.6 525.5 Subcontractor Costs (484.3 ) (540.5 ) (144.0 ) (134.6 ) (278.5 ) (136.8 ) (415.3 ) (88.4 ) (503.7 ) (93.4 ) Net Revenue 1,816.4 2,083.7 647.4 564.3 1,211.7 572.6 1,784.3 540.5 2,324.9 432.1 CIG Segment Revenue 2,292.7 2,634.4 644.9 637.8 1,282.6 676.6 1,959.1 721.2 2,680.2 704.2 Subcontractor Costs (358.0 ) (396.2 ) (94.9 ) (98.3 ) (193.2 ) (96.1 ) (289.4 ) (98.3 ) (387.7 ) (99.1 ) Net Revenue 1,934.7 2,238.2 550.0 539.5 1,089.4 580.5 1,669.7 622.9 2,292.5 605.1 Reconciliation of Net Income Attributable to Tetra Tech to Adjusted EBITDA (in thousands) 2025 2026 2023 2024 1st Qtr 2nd Qtr 6 Mos 3rd Qtr 9 Mos 4th Qtr Full Year 1st Qtr Net Income Attributable to Tetra Tech 273,420 333,382 747 5,388 6,135 113,844 119,979 127,745 247,724 105,028 Income Tax Expense 127,526 130,023 14,530 25,700 40,230 42,815 83,045 46,624 129,668 36,354 Interest Expense 1 46,537 37,271 7,218 8,491 15,709 8,287 23,996 6,806 30,802 7,128 Depreciation 19,980 23,722 5,402 5,248 10,650 5,410 16,059 5,115 21,175 5,608 Amortization 41,226 49,955 10,660 8,629 19,289 8,287 27,577 9,524 37,101 8,387 FX Hedge Gain (89,402 ) - - - - - - - - - Gain on sale of divested business - - - - - - - - - (7,710 ) EBITDA 419,287 574,353 38,557 53,456 92,013 178,643 270,656 195,814 466,470 154,795 Contingent Consideration 12,255 2,541 (366 ) (1,931 ) (2,297 ) (58 ) (2,355 ) (9,873 ) (12,228 ) (7,447 ) Goodwill Impairment - - - 92,416 92,416 - 92,416 - 92,416 - Acquisition & Integration Expenses 2 49,554 7,138 - - - - - - - - Legal Contingency Costs - - 115,000 - 115,000 - 115,000 - 115,000 - Adjusted EBITDA 481,096 584,032 153,191 143,941 297,132 178,585 475,717 185,941 661,658 147,348 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

the item shown at left

other guidance in this release

Text is the filed exhibit, verbatim.