Exhibit 5.1

OPINION OF WILSON SONSINI GOODRICH & ROSATI

PROFESSIONAL CORPORATION

May 23, 2016

CareDx, Inc.

3260 Bayshore Boulevard

Brisbane, California 94005

(415) 287-2300

Re: Registration Statement on Form S-8

Ladies and Gentlemen:

We have examined the Registration Statement on Form S-8 (the “Registration Statement”) to be filed by CareDx, Inc., a Delaware corporation, (the “Company”) with the Securities and Exchange Commission on or about the date hereof, in connection with the registration under the Securities Act of 1933, as amended, of an aggregate of 155,500 shares of Company’s common stock, par value $0.001 per share (the “Shares”), reserved for issuance pursuant to the Company’s 2016 Inducement Equity Incentive Plan (the “2016 Plan”). As your legal counsel, we have reviewed the actions proposed to be taken by you in connection with the issuance and sale of the Shares to be issued under the 2016 Plan.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the Shares, when issued and sold in the manner referred to in the 2016 Plan and pursuant to the agreements that accompany the 2016 Plan, will be legally and validly issued, fully paid and nonassessable.

We consent to the use of this opinion as an exhibit to the Registration Statement and further consent to the use of our name wherever appearing in the Registration Statement and any amendments thereto.

Very truly yours,

/s/ WILSON SONSINI GOODRICH & ROSATI

WILSON SONSINI GOODRICH & ROSATI

Professional Corporation