According to preliminary votes from the Louisiana secretary of state, the vote count as of 10:30 p.m. ET was Kennedy with 64% of the vote, at 466,412, and Democrat Foster Campbell with 36%, at 266,673.
It was the final Senate race of the 2016 election cycle, and the seat had been considered safely Republican in the deep red Southern state. The Republicans now hold a slim majority of 52 seats in the Senate.
Saturday's contest comes after no one candidate captured a majority of the votes in November, a requirement of state law to avoid a runoff. The field originally had two dozen candidates including former Ku Klux Klan leader David Duke
The top two vote finishers
were Kennedy, the state treasurer, with 25% of the vote and Campbell, who had 17.5% of the vote.
Trump stumped for Kennedy
President-elect Donald Trump held a rally Friday in Baton Rouge, asking his supporters to back Kennedy in the election and calling him "a tax cutter" and "true fighter."
"This is an amazing state and tomorrow we need you to go to the polls and send John Kennedy to the United States Senate, and that's why I'm down here," he said. "He's a great guy."
"We need John in Washington not only for the vote, we need (him) for leadership and everything else -- but if you go there we'll win," Trump added. "Kennedy is a proven leader who's balanced -- which is amazing -- 16 budgets (and) returned millions of dollars to taxpayers."
Vice President-elect Mike Pence also campaigned for Kennedy earlier this week.
"By electing John Kennedy your next senator, you're going to put an exclamation point at the end of a great American victory in 2016," Pence told a rally, according to The Times-Picayune newspaper in New Orleans.
Incumbent Republican Sen. David Vitter decided not to run for re-election after losing the 2015 gubernatorial race to Democrat John Bel Edwards.