King won Maine’s 2012 Senate election to replace the retiring Republican Olympia Snowe and took office on January 3, 2013. He was reelected to a second term in 2018, following the state’s inaugural instant-runoff voting elections, and won a third term in 2024 against Republican nominee Demi Kouzounas and Democratic nominee David Costello. For committee assignment purposes, he caucuses with the Democratic Party. He is one of two independents in the Senate; the other is Bernie Sanders of Vermont, who also caucuses with the Democrats.