Exhibit 5.1

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

August 24, 2012

LPL Financial Holdings Inc.

75 State Street

Boston, MA 02109

Re: Registration Statement on Form S-8

Ladies and Gentlemen:

This opinion is furnished to you in connection with the registration statement on Form S-8 (the “Registration Statement”), filed on or about the date hereof with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”), for the registration of 2,800,000 shares of Common Stock, $0.001 par value (the “Shares”), of LPL Financial Holdings Inc., a Delaware corporation (the “Company”). The Shares are issuable under the LPL Financial Holdings Inc. 2012 Employee Stock Purchase Plan (the “Plan”).

We are familiar with the actions taken by the Company in connection with the adoption of the Plan. 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, when the Shares have been issued and sold in accordance with the terms of the Plan, the Shares will be validly issued, fully paid and nonassessable.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement. In giving such consent we do not thereby admit that we are included 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