Exhibit 5.1

  Wilson Sonsini Goodrich & Rosati
Professional Corporation 650 Page Mill Road Palo Alto, California 94304-1050 o: (650) 493-9300
f: (650) 493-6811

February 27, 2024

Alector, Inc.

131 Oyster Point Blvd., Suite 600

South San Francisco, California 94080

(415) 231-5660

Re: Alector, Inc. – 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 Alector, Inc., a Delaware corporation, 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 (i) 4,243,984 shares of Common Stock reserved for issuance pursuant to the 2019 Equity Incentive Plan and (ii) 591,397 shares of Common Stock reserved for issuance pursuant to the 2019 Employee Stock Purchase Plan (which plans are referred to herein as the “Plans” and which shares of Common Stock are referred to herein as the “Shares”).

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 Plans and pursuant to the agreements that accompany the Plans, 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,

WILSON SONSINI GOODRICH & ROSATI

Professional Corporation

/s/ Wilson Sonsini Goodrich & Rosati P.C.