State Rep. Haley, 38, won 62.2 percent of the vote in the runoff.
She was the first Indian-American to hold office in the Palmetto state and also became its first female Republican nominee for governor.
Haley -- endorsed by Republican heavyweights such as Sarah Palin and Mitt Romney -- faced allegations of marital infidelity during her campaign from two men, one an influential South Carolina political blogger and the other a state lobbyist who advised a rival campaign.
AP
His move followed claims by political blogger Will Folks that he had an "inappropriate physical relationship" with Haley several years ago while she was married.
Meanwhile, in North Carolina, Secretary of State Elaine Marshall defeated former state Sen. Cal Cunningham in a Tuesday runoff.
Marshall was expected to face an uphill battle to defeat incumbent Republican Sen. Richard Burr this November.
Also in South Carolina, Tim Scott was leading against Paul Thurmond -- son of the late U.S. senator and former segregationist Strom Thurmond -- giving himself a good shot at being the first black GOP congressman for his state in more than a century.
No black Republican held a seat in Congress after Oklahoma Rep. J.C. Watts left in 2003.
Elections were also being held Tuesday in Utah and Mississippi.