Exhibit 99.1

MONTROSE ENVIRONMENTAL GROUP ANNOUNCES STRONG

FOURTH QUARTER AND FULL YEAR 2020 RESULTS

- Growing Demand for Montrose’s Innovative Environmental Solutions—

- Provides Full Year 2021 Growth Outlook—

IRVINE, California (March 24, 2021) – Montrose Environmental Group, Inc. (the “Company,” “Montrose” or “MEG”) (NYSE: MEG) today announced results for the fourth quarter and full year ended December 31, 2020 and provided its full year 2021 outlook.

Full Year and Fourth Quarter 2020 Highlights

“Fourth quarter and full year results were terrific, reflecting the resiliency in our diversified business and growing demand for our innovative environmental solutions,” stated Vijay Manthripragada, Montrose’s Chief Executive Officer. “Our strong fourth quarter capped our debut year as a public company. We produced record total revenue, generated net income and delivered record Adjusted EBITDA and Adjusted EBITDA margin for the quarter. We built on our existing customer relationships and expanded our market share. We continued our high growth trajectory and we are particularly pleased with our delivery of 17% combined organic growth, including organic growth from CTEH, our environmental response business, for the full fiscal year 2020; exclusive of CTEH, our organic growth was 4%². Our strong performance with a challenging COVID-19 backdrop in 2020 is a testament to the excellence and dedication of our employees for whom I am very grateful.”

Mr. Manthripragada continued, “We believe the emphasis placed on better environmental stewardship by our customers, by our communities, by the capital markets, and by regulators will continue to drive our industry forward. Though we are resilient across political cycles, we expect the environmental priorities of the current U.S. Congress and presidential administration to further accelerate our momentum. In addition, we believe the capital we allocated to research, development and innovation is contributing to our organic growth and benefitting our customers and shareholders. As a result, we are confident in our ability to continue delivering strong organic growth and accretive acquisitions that advance our objective of becoming the leading global environmental solutions provider.”

Fourth Quarter 2020 Results

Total revenue in the fourth quarter of 2020 increased 60.2% to $108.7 million, compared to $67.9 million in the prior year quarter. Excluding discontinued services, which contributed no revenue in the fourth quarter 2020 and $2.9 million in the fourth quarter 2019, total revenue increased 67.2%. The increase in revenues was driven by the acquisition of CTEH in April 2020 and organic growth in our Measurement and Analysis segment, partially offset by a decrease in revenues in our Remediation and Reuse segment. Revenue in all segments was impacted by COVID-19, primarily in the form of delays in project start dates, partially offset by COVID-19 related projects performed by CTEH.

Net income was $0.8 million, compared to a net loss of $11.3 million in the prior year quarter. The year-over-year change was primarily attributable to an increase in both revenues and margins, as well as lower expenses related to fair value adjustments to certain financial instruments and contingent earn-out payments, partially offset by higher tax expense.

Adjusted EBITDA¹ increased to $18.3 million, compared to $10.5 million in the prior year quarter. The increase in Adjusted EBITDA¹ was primarily driven by higher revenues and favorable shifts in business mix. Adjusted EBITDA margin¹ improved 130 basis points to 16.8%, compared to 15.5% in the prior year quarter, mainly due to business mix, operating leverage at the segment level and temporary cost containment measures in response to COVID-19.

Full Year 2020 Results

Total revenue in the full year 2020 increased 40.4% to $328.2 million, compared to $233.9 million in the prior year period. Excluding discontinued services, which generated revenues of $3.8 million and $18.4 million in the full year 2020 and 2019, respectively, total revenue increased 50.5% due to acquisitions and organic growth. Increased revenues in our Measurement and Analysis and Remediation and Reuse segments was attributable to organic growth and acquisitions. Growth in our Assessment, Permitting and Response segment was due to the acquisition of CTEH.

Net loss was $57.9 million, compared to a net loss of $23.6 million in the prior year period. The year-over-year difference in net loss primarily reflected an increase in net expenses from fair value adjustments to certain financial instruments and contingent earn-out payments, as well as from expenses associated with the Company’s initial public offering.

Adjusted EBITDA^{1 increased 74.4% to $54.5 million, compared to $31.2 million in the prior year. The increase in Adjusted EBITDA1 was primarily due to higher revenues and favorable shifts in business mix. Adjusted EBITDA margin1 improved 320 basis points to 16.6%, compared to 13.4% in the prior year period.}

Cash provided by operating activities for the full year ended December 31, 2020 was $1.9 million, compared to cash provided by operating activities of $17.0 million in the prior year. The change between periods mainly reflects an increase in working capital investments of $12.8 million, higher contingent earnout payments of $6.4 million, higher non-capitalized IPO and secondary offering-related costs of $7.0 million, and higher interest payments of $6.1 million. Excluding acquisition-related contingent earnout payments and non-capitalized IPO-related costs, which are not part of recurring operations, cash flow provided by operating activities decreased $1.8 million versus the prior year, primarily due to higher receivables caused by significant fourth quarter revenue growth. Overall days sales outstanding at December 31, 2020, remained unchanged compared to the prior year.

Liquidity and Capital Resources

In October 2020, Montrose improved its borrowing costs through the repricing of its $175.0 million term loan facility which matures in 2025. The interest rate spread on the term loan was reduced by 50 basis points to LIBOR, with a 1.00% floor, plus 4.50%, compared to the prior rate of LIBOR, with a 1.00% floor, plus 5.00%.

At December 31, 2020, Montrose had total debt, net of deferred debt issuance costs, of $175.9 million and $84.4 million of liquidity, including $34.4 million of cash and $50.0 million of availability on its revolving credit facility. As of December 31, 2020, the Company’s leverage ratio under its credit facility, which includes the impact of acquisition-related contingent earnout payments that may become payable in cash, was 2.7 times. Excluding contingent earnout payments of $4.4 million related to CTEH estimated 2021 earnings, an amount which may vary given the environmental emergency response nature of their work, the Company’s leverage ratio was 2.6 times.

Acquisitions

In January 2021, Montrose acquired MSE Group (“MSE”), a leading provider of environmental services primarily to the U.S. federal government. The addition of the MSE team is strategically additive to our Remediation and Reuse Segment, increases our environmental service offerings for select U.S. federal agencies, and expands our geographic presence in the Southeast U.S. The Company’s M&A pipeline and outlook for deal activity in 2021 remain strong.

Full Year 2021 Outlook

The Company is introducing its full year 2021 outlook for Adjusted EBITDA¹ to be in the range of $61 million to $67 million, reflecting anticipated year-over-year revenue growth of approximately 20% at the mid-point. The Company expects Adjusted EBITDA margin¹ to be in the range of 16.0% to 17.0% for full year 2021.

The current outlook is based on a combination of mid-to-high single digit organic growth plus the contribution of completed acquisitions. The outlook does not include any benefit from future acquisitions that have not yet been completed.

We have successfully grown revenue in excess of 20% every year and expect to meet or exceed that threshold in 2021. In addition, we expect to continue adding strategically and financially accretive acquisitions that are not yet reflected in our 2021 guidance or outlook. Because demand for environmental services is not driven by specific or predictable patterns in one or more fiscal quarters, the Company’s business is better assessed on yearly results.

Webcast and Conference Call

The Company’s senior management will host a webcast and conference call on Wednesday, March 24, 2021 at 5:00 p.m. Eastern time to discuss fourth quarter and full year financial results. Their prepared remarks will be followed by a question and answer session. A live webcast of the conference call will be available in the Investors section of the Montrose website at www.montrose-env.com. The conference call will also be accessible by dialing 1-877-407-9208 (Domestic) and 1-201-493-6784 (International). For those who are unable to listen to the live broadcast, an audio replay of the conference call will be available on the Montrose website for 30 days.

About Montrose

Montrose is a leading environmental solutions company focused on supporting commercial and government organizations as they deal with the challenges of today, and prepare for what’s coming tomorrow. With approximately 2,000 employees across over 70 locations around the world, Montrose combines deep local knowledge with an integrated approach to design, engineering, and operations, enabling the Company to respond effectively and efficiently to the unique requirements of each project. From comprehensive air measurement and laboratory services to regulatory compliance, emergency response, permitting, engineering, and remediation, Montrose delivers innovative and practical solutions that keep its clients on top of their immediate needs – and well ahead of the strategic curve. For more information, visit www.montrose-env.com.

Forward-Looking Statements

This press release contains 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 the Company’s 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. Further, many of these factors are, and may continue to be, amplified by the COVID-19 pandemic. Additional factors or events that could cause actual results to differ may also emerge from time to time, and it is not possible for the Company to predict all of them. Forward-looking statements speak only as of the date on which they are made, and the Company undertakes 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 the Company’s filings with the Securities and Exchange Commission, including its Annual Report on Form 10-K for the year ended December 31, 2020, for additional information regarding the risks and uncertainties that may cause actual results to differ materially from those expressed in any forward-looking statement.

Contact Information:

Investor Relations:

Rodny Nacier

(949) 988-3383

ir@montrose-env.com

Media Relations:

Doug Donsky

(646) 361-1427

Montrose@icrinc.com

MONTROSE ENVIRONMENTAL GROUP, INC.

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS

(In thousands, except per share data)

MONTROSE ENVIRONMENTAL GROUP, INC.

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION

(In thousands, except share data)

MONTROSE ENVIRONMENTAL GROUP, INC.

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS

(In thousands)

Non-GAAP Financial Information

In addition to our results under GAAP, in this release we also present certain other supplemental financial measures of financial performance that are not required by, or presented in accordance with, GAAP, including Adjusted EBITDA and Adjusted EBITDA margin. We calculate Adjusted EBITDA as net income (loss) before interest expense, income tax expense (benefit) and depreciation and amortization, adjusted for the impact of certain other items, including stock-based compensation expense and acquisition-related costs, as set forth in greater detail in the table below. Adjusted EBITDA margin represents Adjusted EBITDA as a percentage of revenues for a given period.

Adjusted EBITDA and Adjusted EBITDA margin are two of the primary metrics used by management to evaluate our financial performance and compare it to that of our peers, evaluate the effectiveness of our business strategies, make budgeting and capital allocation decisions and in connection with our executive incentive compensation. These measures are also frequently used by analysts, investors and other interested parties to evaluate companies in our industry. Further, we believe they are helpful in highlighting trends in our operating results because they allow for more consistent comparisons of financial performance between periods by excluding gains and losses that are non-operational in nature or outside the control of management, as well as items that may differ significantly depending on long-term strategic decisions regarding capital structure, the tax jurisdictions in which we operate and capital investments.

These non-GAAP measures do, however, have certain limitations and should not be considered as an alternative to net income (loss) or any other performance measure derived in accordance with GAAP. Our presentation of Adjusted EBITDA and Adjusted EBITDA margin should not be construed as an inference that our future results will be unaffected by unusual or non-recurring items for which we may make adjustments. In addition, Adjusted EBITDA and Adjusted EBITDA margin may not be comparable to similarly titled measures used by other companies in our industry or across different industries, and other companies may not present these or similar measures. Management compensates for these limitations by using these measures as supplemental financial metrics and in conjunction with our results prepared in accordance with GAAP. We encourage investors and others to review our financial information in its entirety, not to rely on any single measure and to view Adjusted EBITDA and Adjusted EBITDA margin in conjunction with the related GAAP measures.

Additionally, we have provided estimates regarding Adjusted EBITDA and Adjusted EBITDA margin for 2021. These projections account for estimates of revenue, operating margins and corporate and other costs. However, we cannot reconcile our projection of Adjusted EBITDA to net income (loss), the most directly comparable GAAP measure, without unreasonable efforts because of the unpredictable or unknown nature of certain significant items excluded from Adjusted EBITDA and the resulting difficulty in quantifying the amounts thereof that are necessary to estimate net income (loss). Specifically, we are unable to estimate for the future impact of certain items, including income tax (expense) benefit, stock-based compensation expense, fair value changes and the accounting for the issuance of the Series A-2 preferred stock. We expect the variability of these items could have a significant impact on our reported GAAP financial results.

In this release we also provide information regarding organic growth, which is one of the measures management uses to asses our results of operations. We define organic growth as the change in revenues excluding revenues from acquisitions for the first twelve months following the date of acquisition and excluding revenues from businesses disposed of or discontinued. As a result of the significance of the CTEH acquisition to Montrose, and the potential annual volatility in CTEH’s revenues, we also disclose organic growth combined with the annual organic revenue growth of CTEH, but excluding CTEH’s revenues from projects contributing more than $4 million of revenue. We expect to continue to disclose organic revenue growth with and without CTEH. Organic growth is not, however, a measure of revenue growth calculated in accordance with GAAP and should be considered in conjunction with revenue growth calculated in accordance with GAAP.

Montrose Environmental Group, Inc.

Reconciliation of Net Loss to Adjusted EBITDA

(in thousands)