The 1964 United States Senate election in Montana took place on November 3, 1964. Incumbent United States Senator
1958, ran for re-election. Mansfield won the Democratic primary in a landslide, and advanced to the general election, where he faced Alex Blewett, the Majority Leader of the Montana House of Representatives and the Republican
nominee. Though Mansfield's margin was quite reduced from 1958, he still overwhelmingly defeated Blewett and won his third term in the Senate in a landslide.