Nearly two dozen allies flanked Mr Trump during his victory speech
Flanked at his podium on the Columbia state fairgrounds by nearly two dozen allies, including most of the state's political leaders, he told a raucous crowd: "This was a little sooner than we anticipated."
Mr Trump certainly has much to boast about with this win. Exit polling conducted by the BBC's US partner, CBS News, shows that the ex-president bested Ms Haley with both men and women, and among all age groups.
Lauding them for their support, Mr Trump, 77, reminded his audience: "We have a lot of work ahead of us."
But it does not seem he will be able to fully turn his attention to the general election just yet.
Ms Haley re-committed to staying in the race until at least Super Tuesday - 5 March - when voters in 16 states will cast their ballots on the same day.
"I'm a woman of my word," the former UN ambassador said. "We're headed to Michigan tomorrow, and we're headed to the Super Tuesday states throughout all of next week."
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The former president also remains beleaguered by his many legal troubles, and faces the first of four criminal trials next month
He is also now on the hook for more than half a billion dollars, the combined total of two recent civil trial rulings against him in New York - one for sexual assault and defamation, and another for business fraud.
As Mr Biden racks up a sizeable cash advantage over him in what will likely be the most expensive presidential race in US history, Mr Trump is increasingly relying on donations to cover his soaring legal costs.
It appears the Republican Party could come to his aid. He has consolidated his hold over it by endorsing key allies to lead its national committee.
His daughter-in-law Lara Trump, his pick to take over as co-chair of the Republican Party, has pledged to "spend every penny" of party funds on his legal defence.
