2018 United States Senate election in Montana

Incumbent Democratic Senator Jon Tester was reelected to a third term, defeating Republican State Auditor Matt Rosendale.

Following his loss, Rosendale went on to run for Montana's vacant congressional seat in 2020 and won, taking office in the U.S. House of Representatives in January 2021.

Breckenridge said that he realistically anticipated only receiving three or four percent of the vote in the general election, and that he endorsed Rosendale's efforts to stop the use of dark money in politics.

[46][47][48] Kelly won the Green Party nomination, but a Montana district court judge ruled that he had insufficient signatures to get on the ballot.

[49] From Secretary of State of Montana[107] Votes Counties that flipped from Democratic to Republican Official campaign websites

Results by county
Map legend
  • Rosendale—60–70%
  • Rosendale—50–60%
  • Rosendale—40–50%
  • Rosendale—30–40%
  • Rosendale—<30%
  • Rosendale/Fagg tie—30–40%
  • Fagg—30–40%
  • Fagg—40–50%
  • Fagg—50–60%
  • Olszewski—30–40%
  • Olszewski—40–50%
Results by county
Map legend
  • Kelly—100%
  • Kelly—≥90%
  • Kelly—80–90%
  • Kelly—70–80%
  • Kelly—60–70%
  • Kelly—50–60%
  • Kelly—40–50%
  • Kelly/Adams tie—30–40%
  • Kelly/Adams tie—50%
  • Adams—50–60%
  • Adams—60–70%
  • Adams—100%
  • No votes
Swing by county
Legend
  • Democratic—+10-15%
  • Democratic—+5-10%
  • Democratic—+<5%
  • Republican—+<5%
  • Republican—+5-10%
  • Republican—+10-15%
  • Republican—+15-20%
  • Republican—+20-25%
State House district results
State Senate district results