POWER OF ATTORNEY

With respect to holdings of and transactions in securities issued by Guardant
Health, Inc. (the "Company"), the undersigned hereby constitutes and appoints
the individuals named on Schedule A attached hereto and as may be amended from
time to time, or any of them signing singly, with full power of substitution and
resubstitution, to act as the undersigned's true and lawful attorney-in-fact to:
1.    prepare, execute in the undersigned's name and on the undersigned's behalf,
and submit to the United States Securities and Exchange Commission (the "SEC") a
Form ID, including amendments thereto, and any other documents necessary or
appropriate to obtain and/or regenerate codes and passwords enabling the
undersigned to make electronic filings with the SEC of reports required by
Section 16(a) of the Securities Exchange Act of 1934, as amended, or any rule or
regulation of the SEC;
2.    execute for and on behalf of the undersigned, Forms 3, 4, and 5 in accordance
with Section 16 of the Securities Exchange Act of 1934, as amended, and the
rules thereunder;
3.    do and perform any and all acts for and on behalf of the undersigned which
may be necessary or desirable to complete and execute any such Form 3, 4, or 5,
complete and execute any amendment or amendments thereto, and timely file such
form with the SEC and any stock exchange or similar authority; and
4.    take any other action of any type whatsoever in connection with the foregoing
which, in the opinion of such attorney-in-fact, may be of benefit to, in the
best interest of, or legally required by, the undersigned, it being understood
that the documents executed by such attorney-in-fact on behalf of the
undersigned pursuant to this Power of Attorney shall be in such form and shall
contain such terms and conditions as such attorney-in-fact may approve in such
attorney-in-facts discretion.
The undersigned hereby grants to each such attorney-in-fact full power and
authority to do and perform any and every act and thing whatsoever requisite,
necessary, or proper to be done in the exercise of any of the rights and powers
herein granted, as fully to all intents and purposes as the undersigned might or
could do if personally present, with full power of substitution and
resubstitution or revocation, hereby ratifying and confirming all that such
attorney-in-fact, or such attorneys-in-fact substitute or substitutes, shall
lawfully do or cause to be done by virtue of this Power of Attorney and the
rights and powers herein granted.
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 any
Company assuming, any of the undersigned's responsibilities to comply with
Section 16 of 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.
[Signature Page Follows]

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be
executed as of this 1st day of December, 2020.



By:    /s/ Michael Bell
Name:     Michael Bell

Schedule A

Individuals Appointed as Attorney-in-Fact with Full Power of Substitution and
Resubstitution

1.    John Saia