Incumbent Democratic Senator Jon Tester lost re-election to a fourth term, being defeated by Republican nominee Tim Sheehy.

Tester was widely seen as being the most vulnerable incumbent running for re-election, due to Montana's strong Republican lean and the decline of split-ticket voting.

[5] Montana has generally been considered a red state at the federal executive level, voting for Republican candidates in each presidential election starting in 1996, when Bob Dole beat Bill Clinton by nearly 3 percentage points in a three-way race with Ross Perot.

Tester refused to endorse fellow Democrat Kamala Harris for president, a contributing factor towards the Senate race having been considered less nationalized.

The bill's sponsor, Republican Greg Hertz, said it would require the winner of the 2024 Senate race to receive a majority of the vote.

Both Democrats and Libertarians alleged the bill was intended to prevent the Libertarian Party from placing a nominee on the general election ballot in the Senate race who could potentially pull votes away from the Republican nominee, with Democratic state senator Ryan Lynch calling it a "partisan power grab.

"[11][12] After the bill received backlash, Hertz introduced an amendment to make the use of a top-two primary for U.S. Senate elections permanent rather than sunsetting it after the 2024 race.