The 1972 United States Senate election in Maine was held on November 7, 1972. Incumbent Republican U.S. Senator Margaret Chase Smith ran for re-election to a fifth term, but was defeated by Democrat William Hathaway. As of 2022, this was the last time the Democrats won the Class 2 Senate seat from Maine. As of 2022, this remains one of only two times in history (along with the 1846 election) that a Democrat has been elected to this seat for a full term, and the only such instance since the founding of the Republican Party.