Justin Sadrian Form 3 AVALARA / JUSTIN SADRIAN ownership change

                               POWER OF ATTORNEY

      The undersigned, Justin L. Sadrian, hereby constitutes and appoints each
of William D. Ingram, Daniel E. Manning, and Alesia L. Pinney, acting
individually or jointly, with full power of substitution and resubstitution, to
have full power and authority to act in his name, place, and stead and on the
undersigned's behalf as his true and lawful attorney-in-fact to:

     (1)    execute and deliver for and on behalf of the undersigned Forms 3, 4
            and 5 (including any amendments, corrections, supplements or other
            changes thereto) in accordance with Section 16(a) of the Securities
            Exchange Act of 1934, as amended (the "Exchange Act"), and the rules
            thereunder;

     (2)    do and perform any and all acts for and on behalf of the undersigned
            that may be necessary or desirable to complete and execute any such
            Forms 3, 4 or 5 (including any amendments, corrections, supplements
            or other changes thereto) and timely file such Forms with the United
            States Securities and Exchange Commission and any stock exchange,
            self-regulatory association or any other authority or person as may
            be required by law; and

     (3)    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 of, 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 his discretion.

      The undersigned hereby grants to each attorney-in-fact full power and
authority to do and perform all and every act and thing whatsoever requisite,
necessary and proper to be done in the exercise of any of the rights and powers
herein granted, as fully to all intents and purposes as such attorney-in-fact
might or could do if personally present, with full power of substitution or
revocation, hereby ratifying and confirming all that such attorney-in-fact, or
his 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 either
Avalara, Inc., or any affiliates or subsidiaries thereof, assuming, (i) any of
the undersigned's responsibilities to comply with the requirements of the
Exchange Act or any liability for the undersigned's failure to comply with such
requirements or (ii) any obligation or liability that the undersigned incurs for
profit disgorgement under Section 16(b) of the Exchange Act.

      This Power of Attorney shall continue in full force and effect until
revoked by the undersigned in a signed writing delivered to the foregoing
attorneys-in-fact or by such attorneys-in-fact in a signed writing delivered to
the undersigned.  This Power of Attorney hereby revokes any previous Power of
Attorney granted by the undersigned with respect to the matters contained
herein.

      IN WITNESS WHEREOF, the undersigned has executed this Power of Attorney
this 30th day of May, 2018.

                                        Signature: /s/ JUSTIN L. SADRIAN
                                                   ----------------------
                                        Name:      Justin L. Sadrian