Mont. Const. art. VI, § 14

(1) If the governor-elect is disqualified or dies, the lieutenant governor-elect upon qualifying for the office shall become governor for the full term. If the governor-elect fails to assume office for any other reason, the lieutenant governor-elect upon qualifying as such shall serve as acting governor until the governor-elect is able to assume office, or until the office becomes vacant.

(2) The lieutenant governor shall serve as acting governor when so requested in writing by the governor. After the governor has been absent from the state for more than 45 consecutive days, the lieutenant governor shall serve as acting governor.

(3) He shall serve as acting governor when the governor is so disabled as to be unable to communicate to the lieutenant governor the fact of his inability to perform the duties of his office. The lieutenant governor shall continue to serve as acting governor until the governor is able to resume the duties of his office.

(4) Whenever, at any other time, the lieutenant governor and attorney general transmit to the legislature their written declaration that the governor is unable to discharge the powers and duties of his office, the legislature shall convene to determine whether he is able to do so.

(5) If the legislature, within 21 days after convening, determines by two-thirds vote of its members that the governor is unable to discharge the powers and duties of his office, the lieutenant governor shall serve as acting governor. Thereafter, when the governor transmits to the legislature his written declaration that no inability exists, he shall resume the powers and duties of his office within 15 days, unless the legislature determines otherwise by two-thirds vote of its members. If the legislature so determines, the lieutenant governor shall continue to serve as acting governor.

(6) If the office of governor becomes vacant by reason of death, resignation, or disqualification, the lieutenant governor shall become governor for the remainder of the term, except as provided in this constitution.

(7) Additional succession to fill vacancies shall be provided by law.

(8) When there is a vacancy in the office of governor, the successor shall be the governor. The acting governor shall have the powers and duties of the office of governor only for the period during which he serves.