The former president had been widely favored to win the Southern state, despite his litany of criminal charges and Haley's status as a native of South Carolina who won two terms as governor.
The big win will bolster calls from Trump's allies that Haley, Trump's last remaining challenger, should drop out of the race. But Haley, who appeared to have outperformed expectations based on opinion polls, again defiantly insisted she would fight on at least through "Super Tuesday" on March 5, when Republicans in 15 states and one U.S. territory will cast ballots.
Trump was leading 60.0% to 39.4%, a margin of 20.6 percentage points, with about 83% of the expected vote tallied, according to Edison. Statewide opinion polls prior to Saturday had given Trump an average lead of 27.6 percentage points, according to the tracking website 538.