Prior to his election to the state senate, he was the County Attorney for
Brookings County, South Dakota. He served in the
South Dakota State Senate from 1963 to 1968 representing the 13th district (1963–66) and the 6th district (1967–68). He was later a judge on the South Dakota Third Judicial Circuit. On April 10, 1968, Mydland was the fourth candidate for the Republican nomination for Attorney General. He joined previously announced candidates Walter Andre, Michael Strain both of Pierre and assistant attorneys general and Tony Wiesensee an attorney from Canton. On July 16, 1968, at the Republican Convention, Mydland defeated Michael Strain by a vote of 82,946 to 48,764; Andre and Wiesensee removed themselves from the race before the voting began. Mydland was elected as Attorney General by defeating Democrat
James Abourezk in 1968. Gordon received 148,366 (55.69%) votes; James received 118,045 (44.31%) votes. Mydland was challenged for re-nomination by Ron Schmidt of Pierre. Mydland prevailed with 118,446 1/2 votes to Schmidt receiving 42,542 1/2 votes. Mydland was re-elected in 1970 by defeating Democrat Ramon Roubideaux. Gordon received 116,493 (50.40%) votes; Ramon received 114,633 (49.60%) votes. Secretary of State
Alma Larson endorsed Mydland for the nomination runoff. Ultimately, Robert Hirsch was nominated by the convention for the US Senate, but he lost to Democrat
James Abourezk in the general election. In 1977, Mydland was appointed to be a Circuit Court judge for the 3rd Judicial Circuit, where he served until his retirement in 1987. ==Personal life and death==