Investor Presentation November 2023

Safe Harbor Statements contained herein and in the accompanying oral presentation contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. Forward-looking statements may be identified by the use of words such as “intend," "expect", and "may", and other similar expressions that predict or indicate future events or that are not statements of historical matters. Forward-looking statements are based on current information available at the time the statements are made and on management's reasonable belief or expectations with respect to future events, and are subject to risks and uncertainties, many of which are beyond Montrose Environmental Group, Inc.'s ("Montrose," "we,” “us” and “our”) control, that could cause actual performance or results to differ materially from the belief or expectations expressed in or suggested by the forward-looking statements. Additional factors or events that could cause actual results to differ may also emerge from time to time, and it is not possible for us to predict all of them. Forward-looking statements speak only as of the date on which they are made, and we undertake no obligation to update any forward-looking statement to reflect future events, developments or otherwise, except as may be required by applicable law. Investors are referred to Montrose's filings with the Securities and Exchange Commission, including its Annual Report on Form 10-K for the year ended December 31, 2022, for additional information regarding the risks and uncertainties that may cause actual results to differ materially from those expressed in any forward-looking statement. Included in this presentation and the accompanying oral presentation are certain financial measures that are not calculated in accordance with U.S. generally accepted accounting principles ("GAAP") designed to supplement, and not substitute, Montrose's financial information presented in accordance with GAAP. The non-GAAP measures as defined by Montrose may not be comparable to similar non-GAAP measures presented by other companies. The presentation of such measures, which may include adjustments to exclude unusual or non-recurring items, should not be construed as an inference that Montrose's future results, cash flows or leverage will be unaffected by other unusual or nonrecurring items. Please see the appendix to this presentation for how we define these non- GAAP measures, a discussion of why we believe they are useful to investors and certain limitations thereof, reconciliations for historical periods thereof to the most directly comparable GAAP measures and certain matters related to forward-looking non-GAAP information. The data included in this presentation regarding markets and the industry in which we operate, including the size of certain markets, are based on publicly available information, reports of government agencies, and published industry sources such as Environmental Business International, Inc. ("EBI"). In presenting this information, we have also made certain estimates and assumptions that we believe to be reasonable based on the information referred to above and similar sources, as well as our internal research, calculations and assumptions based on our analysis of such information and our knowledge of, and our experience to date in, our industries and markets. Market share data is subject to change and may be limited by the availability of raw data, the voluntary nature of the data gathering process and other limitations inherent in any statistical survey of market share data. In addition, customer preferences are subject to change. Accordingly, you are cautioned not to place undue reliance on such market share data or any other such estimates. While we believe such information is reliable, we cannot guarantee the accuracy or completeness of this information, and have we independently verified any third-party information and data from our internal research has not been verified by any independent source. © 2023 Montrose Environmental Group, Inc. Proprietary. | 2

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