Prior to serving as governor, Mickelson, a
Republican, served as State's Attorney for Walworth County from 1933 to 1936. He served in the
South Dakota House of Representatives from 1937 to 1943 and was Speaker of the House in his last term. He then served as
South Dakota Attorney General from 1943 to 1947.
1942 Attorney General election On May 9, 1942, Mickelson announced his candidacy for Attorney General. On June 8, 1942, Mickelson won the nomination at the convention in a field of five candidates on the second vote with 110,090 votes; 31,359 votes for Harold O. Lovre of Hayti; 17,049 for William J Metzger of Olivet; 6,773 votes for Assistant Attorney General Erwin R. Erickson of Vermillion; and 1,610 votes for E.B. Adams of Hot Springs. Mickelson defeated Democrat Lynn Fellows of Plankinton by a vote count of 108,155 to 62,527 votes.
1944 Attorney General election On February 22, 1944, Mickelson declared that he would run for re-election. On August 1, 1944, Fred Wheeler of Custer was unopposed and nominated for Attorney General at the Democratic Convention in Aberdeen. Mickelson was re-elected defeating Democrat Wheeler by a count of 137,311 to 83,441 votes.
Gubernatorial elections Mickelson became
Governor of South Dakota in 1947, and served until 1951. ==Presidential run==