Tex. Government Code § 401.023: SUCCESSION.

(a) If the governor, lieutenant governor, and president pro tempore of the senate are unavailable, the following officers in succeeding order shall exercise the powers and discharge the duties of the office of governor:

(1) the speaker of the house of representatives;

(2) the attorney general; and

(3) the chief justices of the courts of appeals, in the numerical order of the supreme judicial districts the courts serve.

(b) An officer listed in this section acts as governor under this subchapter only if the preceding officers in the order of succession are unavailable.

Acts 1987, 70th Leg., ch. 147, Sec. 1, eff. Sept. 1, 1987.