POWER OF ATTORNEY

        Know all by these presents, that the undersigned hereby constitutes and
appoints Laura Holm, Seth Goettelman or Ashley Otero with full power of
substitution, as the undersigned's true and lawful attorney-in-fact to:

        (1)     execute for and on behalf of the undersigned, in the
                undersigned's capacity as an officer and/or director of XBiotech
                Inc. or any successor thereto (the "Company"), Forms 3, 4, and 5
                in accordance with Section 16(a) of the Securities Exchange Act
                of 1934 and the rules thereunder (the "Exchange Act"), Form 144
                in accordance with Rule 144 under the Securities Act of 1933
                ("Rule 144") and any other forms or reports, including, but not
                limited to, a Form ID, that the undersigned may be required to
                file in connection with the undersigned's ownership, acquisition
                or disposition of securities of the Company;

        (2)     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, Form 144 or other form or
                report, complete and execute any amendment or amendments thereto
                and timely file such form or report with the Securities and
                Exchange Commission and any stock exchange or similar authority;
                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 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-fact's
                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 or revocation, hereby ratifying and confirming all that such
attorney-in-fact, or such attorney-in-fact's 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 the Company assuming, any of the
undersigned's responsibilities to comply with Section 16 of the Exchange Act or
Rule 144.

        This Power of Attorney revokes any previous Power of Attorney filed with
the Company for the purposes set forth herein and 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 expressly revoked before that time.


        IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to
be executed as of this  6th day of April, 2015.

                                        /s/ John Simard
                                        ---------------------------------------
                                        John Simard