BATON ROUGE, La. — Bringing a wildly unpredictable election cycle to an unsurprising close, Louisiana voters on Saturday elected John Neely Kennedy, the state treasurer, to the Senate, giving Republicans a final 52-48 advantage over the Democrats.

With roughly two-thirds of the precincts reporting, Mr. Kennedy had secured 64 percent of the vote and the seat vacated by Senator David Vitter, defeating Foster Campbell, a public service commissioner long known for his populism.

Mr. Kennedy, with an anti-establishment, outsider message and a reputation as a fiscal hawk, secured a commanding position early in the race in Louisiana, which has not sent a Democrat to the Senate since 2008.

“I’m humbled and honored by the overwhelming support from all over the state,” Mr. Kennedy said on Saturday. “Louisiana voters sent a clear message tonight and I’m ready to go to Washington, D.C., to fight for our people.”