Tim Sheehy, a businessman and former Navy SEAL, won the Republican primary for U.S. Senate in Montana on Tuesday, according to The Associated Press, setting him up for a November showdown against Senator Jon Tester, the Democratic incumbent.

With roughly half of the vote counted, Mr. Sheehy had 73 percent, well ahead of his lesser-known opponents. Brad Johnson, Montana’s former secretary of state, had 19 percent of the vote, and Charles Walkingchild had 7.5 percent.

“As a Navy SEAL, I’ve always put country before self and I’m running for the U.S. Senate to end Joe Biden and Jon Tester’s inflation, seal our border, secure our children’s future, and put America First,” Mr. Sheehy said in a statement, adding that he was “humbled and honored by all the support.”

The Republican primary was essentially a foregone conclusion since February, when Representative Matt Rosendale abruptly exited the race — less than a week after he entered it — citing former President Donald J. Trump’s endorsement of Mr. Sheehy. Mr. Rosendale, a right-wing hard-liner, had been viewed as the only serious challenger to Mr. Sheehy, for whom the Republican establishment had worked to clear the field. His victory is a boon for Republicans as they work to recapture control of the Senate, competing on a favorable map in which a number of vulnerable Democrats face tough re-election battles.

“Tim Sheehy is a strong conservative, an American hero and a successful businessman who will bring an outsider’s perspective to a broken Washington,” said Senator Steve Daines, the Montana Republican who leads the National Republican Senatorial Committee, which works to elect Republicans to the Senate. “The clearest path to a Republican Senate majority runs through Montana.”

Mr. Sheehy will face a formidable opponent in Mr. Tester, a popular incumbent who has survived past challenges in his ruby-red state by leaning on his background as a third-generation Montana farmer and his reputation of bipartisanship. Recent polls have suggested a tight race, and the nonpartisan Cook Political Report rates Montana a “tossup.” Mr. Tester officially captured the Democratic nomination on Tuesday.