Mississippi Code Title 23. Elections § 23-15-855

(1) If a vacancy shall occur in the office of United States Senator from Mississippi by death, resignation or otherwise, the Governor shall, within ten (10) days after receiving official notice of the vacancy, issue a proclamation for an election to be held in the state to elect a Senator to fill the remaining unexpired term, provided the unexpired term is more than twelve (12) months and the election shall be held within ninety (90) days from the time the proclamation is issued and the returns of such election shall be certified to the Governor in the manner set out above for regular elections, unless the vacancy occurs in a year in which a general state or congressional election is held, in which event the Governor's proclamation shall designate the general election day as the time for electing a Senator, and the vacancy shall be filled by appointment as hereinafter provided.

(2) In case of a vacancy in the office of United States Senator, the Governor may appoint a Senator to fill the vacancy temporarily, and if the United States Senate be in session at the time the vacancy occurs the Governor shall appoint a Senator within ten (10) days after receiving official notice thereof, and the appointed Senator shall serve until a successor is elected and commissioned as provided for in subsection (1) of this section, provided that such unexpired term as he or she may be appointed to fill shall be for a longer time than one (1) year, but if for a shorter time than one (1) year, he or she shall serve for the full time of the unexpired term and no special election shall be called by the Governor but a successor shall be elected at the regular election.