The 2008 United States Senate election in South Dakota was held on November 4, 2008. Primary elections were held on June 3, 2008. Incumbent Senator Tim Johnson won re-election to a third term. As of 2024, this election alongside the simultaneous House race is the last time a Democrat won a statewide election in South Dakota. This is the last time that a Senate candidate and a presidential candidate of different political parties simultaneously won South Dakota.

Timothy Peter Johnson is a retired American lawyer and politician who served as a United States senator from South Dakota from 1997 to 2015. A member of the Democratic Party, he served as the United States representative for South Dakota's at-large congressional district from 1987 to 1997 and in the state legislature from 1979 to 1987. He is the last Democrat to hold statewide and/or congressional office in South Dakota. He and Stephanie Herseth are also the last Democrats to win a statewide and/or federal election in South Dakota.