Tennessee Republicans chose Bill Lee, a wealthy businessman who has never served in elected office, as their nominee for governor on Thursday, spurning a conservative candidate who eagerly sought — but only glancingly received — the support of President Trump’s White House.

Mr. Lee prevailed in a field of six candidates, The Associated Press reported, after a primary campaign that collectively cost Republicans about $46 million and previewed an autumn of political turbulence. He will face Karl Dean, a former Nashville mayor who easily won the Democratic primary, in the race to succeed Gov. Bill Haslam, a term-limited Republican.

“Looking back, I never could have imagined that the road would lead here,” Mr. Lee, appearing visibly surprised after a victory that followed a late surge in the polls, said Thursday night.

Although Tennessee is a conservative state that Republican presidential nominees have carried since 2000, Democrats believe they have recruited their strongest candidates in more than a decade. Both parties are preparing to spend millions of dollars on the campaigns for governor and an open Senate seat.