Defined Contribution Plan	9 Months Ended
Sep. 30, 2022
Retirement Benefits [Abstract]
Defined Contribution Plan	20. DEFINED CONTRIBUTION PLAN On January 1, 2014, the Company established the Montrose Environmental Group 401(k) Savings Plan (the “401(k) Savings Plan”). As of September 30, 2022, and December 31, 2021, plan participants may defer up to 85.0% of their eligible wages for the year, up to the Internal Revenue Service dollar limit and catch-up contribution allowed by law. Prior to May 22, 2020, the Company provided employer matching contributions equal to 100.0% of the first 3.0% of the participant’s compensation and 50.0% of the participant’s elective deferrals that exceed 3.0% but do not exceed 4.0% of the participant’s compensation. Beginning on May 22, 2020, the Company temporarily ceased making employer contributions. Employer contributions were reinstated beginning on April 23, 2021. Employer contributions under the 401(k) Savings Plan were $1.2 million and $4.6 million for the three and nine months ended September 30, 2022, respectively, and $0.8 million and $1.6 million for the three and nine months ended September 30, 2021, and are included within selling, general, and administrative expense on the unaudited condensed consolidated statements of operations.

Defined Contribution Plan

9 Months Ended

Sep. 30, 2022

20. DEFINED CONTRIBUTION PLAN

On January 1, 2014, the Company established the Montrose Environmental Group 401(k) Savings Plan (the “401(k) Savings Plan”). As of September 30, 2022, and December 31, 2021, plan participants may defer up to 85.0% of their eligible wages for the year, up to the Internal Revenue Service dollar limit and catch-up contribution allowed by law. Prior to May 22, 2020, the Company provided employer matching contributions equal to 100.0% of the first 3.0% of the participant’s compensation and 50.0% of the

participant’s elective deferrals that exceed 3.0% but do not exceed 4.0% of the participant’s compensation. Beginning on May 22, 2020, the Company temporarily ceased making employer contributions. Employer contributions were reinstated beginning on April 23, 2021. Employer contributions under the 401(k) Savings Plan were $1.2 million and $4.6 million for the three and nine months ended September 30, 2022, respectively, and $0.8 million and $1.6 million for the three and nine months ended September 30, 2021, and are included within selling, general, and administrative expense on the unaudited condensed consolidated statements of operations.