The 1970 United States Senate election in Montana took place on November 3, 1970. Incumbent U.S. Senator
Mike Mansfield, the sitting
Senate majority leader who was first elected to the Senate in
1952 and was re-elected in
1958 and
1964, ran for re-election. Mansfield won the
Democratic primary against several opponents, and advanced to the general election, where he was opposed by Harold E. Wallace, a sporting goods salesman and the
Republican nominee. While his margin of victory decreased slightly from 1964, Mansfield still managed to defeat Wallace in a landslide, winning his fourth and final term in the Senate.