Exhibit 5.1

ROPES & GRAY LLP PRUDENTIAL TOWER 800 BOYLSTON STREET BOSTON, MA 02199-3600 WWW.ROPESGRAY.COM

May 24, 2024

LifeStance Health Group, Inc.

4800 N. Scottsdale Road, Suite 2500

Scottsdale, AZ 85251

Re: Registration Statement on Form S-3 filed on May 21, 2024 (Registration No. 333-279585)

Ladies and Gentlemen:

We have acted as counsel to LifeStance Health Group, Inc., a Delaware corporation (the “Company”) in connection with the sale of up to 23,000,000 shares of common stock, $0.01 par value per share (the “Shares”), of the Company pursuant to the above-referenced registration statement (the “Registration Statement”), filed by the Company with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933 (the “Securities Act”). The Shares are being sold pursuant to an underwriting agreement, dated May 21, 2024, among the Company, Morgan Stanley & Co. LLC and Goldman Sachs & Co. LLC as representatives of the several underwriters named in Schedule I thereto, and the selling stockholders named in Schedule II thereto (the “Selling Stockholders”).

In connection with this opinion letter, we have examined such certificates, documents and records and have made such investigation of fact and such examination of law as we have deemed appropriate in order to enable us to render the opinions set forth herein. In conducting such investigation, we have relied, without independent verification, upon certificates of officers of the Company, public officials and other appropriate persons.

The opinions expressed below are limited to the Delaware General Corporation Law.

Based upon and subject to the foregoing, we are of the opinion that the Shares have been duly authorized and are validly issued, fully paid and non-assessable.

We hereby consent to your filing this opinion as an exhibit to the Registration Statement and to the use of our name therein and in the related prospectus under the caption “Legal Matters.” In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission thereunder.

Very truly yours,

/s/ Ropes & Gray LLP

Ropes & Gray LLP