POWER OF ATTORNEY

    The undersigned, as a Section 16 reporting person of Arcus Biosciences,
Inc., a Delaware corporation (the "Company"), hereby constitutes and appoints
each of the persons listed on Exhibit A attached hereto, signing singly, as the
undersigned's true and lawful attorney-in-fact to:

    (1) complete and execute for and on behalf of the undersigned Forms 3, 4 and
5 and other forms and all amendments thereto as such attorney-in-fact shall in
his or her discretion determined to be required or advisable pursuant to Section
16 of the Securities Exchange Act of 1934 (as amended) and the rules and
regulations promulgated thereunder, or any successor laws and regulations, as a
consequence of the undersigned's ownership, acquisition or disposition of
securities of the Company; and

    (2) do all acts for and on behalf of the undersigned as necessary in order
to file such forms with the Securities and Exchange Commission, any securities
exchange or national association, the Company and such other person or agency as
the attorney-in-fact shall deem appropriate.

    The undersigned hereby ratifies and confirms all that said attorneys-in-fact
and agents shall do or cause to be done by virtue hereof.  The undersigned
acknowledges that the foregoing attorneys-in-fact, in serving in such capacity
at the request of the undersigned, are not assuming, nor is the Company
assuming, any of the undersigned's responsibilities to comply with the
Securities Exchange Act of 1934 (as amended).

    This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms 3, 4, and 5 with respect to the
undersigned's holdings of and transactions in securities issued by the Company,
unless earlier revoked by the undersigned in a signed writing delivered to the
foregoing attorneys-in-fact.

    IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be
executed as of this 9 day of March, 2018.


                                        Alphabet Inc.

                                        By:  /s/ Kent Walker
                                        ----------------------------------------
                                        Name: Kent Walker
                                        Title: Assistant Secretary


                                     EXHIBIT A
                                     ---------

                                 Jennifer Jarrett
                                   Carolyn Tang
                                  Marcia A. Hatch
                                    Heidi Mayon
                                   Colin Conklin
                                   Scott Paraker