Lt. Gov. Henry McMaster, who was elected in November 2014, previously served as the state's attorney general and chairman of the South Carolina GOP. He is the highest-ranking South Carolina official to endorse Trump.
"He's actually done some things. Some big things," McMaster said. "He speaks the truth as he sees it in words everybody can understand."
He told supporters packed into a barn and additional covered patio set up for the event that he and his family would be voting for Trump.
McMaster had previously supported Sen. Lindsey Graham of South Carolina, who dropped out of the presidential race last month after a campaign spent frequently sparring with Trump, who repeatedly criticized the South Carolina senator.
Graham has since endorsed former Florida Gov. Jeb Bush in the GOP race.
In an interview with The Post and Courier
, Graham said Thursday that although he doesn't "know what Henry's thinking is," he admires McMaster.
"He is one of my dearest friends," Graham said. "I think he will be helpful to Mr. Trump. He will give him so legitimacy, sort of, in the establishment lane."
Graham added that the endorsement surprised him "a little bit. But politics is politics."
Richard Quinn, who has been a friend and political consultant to both Graham and McMaster, told CNN on Wednesday that McMaster and Graham are "very close."
Quinn also said McMaster's endorsement is yet another indication that Trump's presidential bid is gaining legitimacy in establishment circles as Trump is perceived more and more as the likeliest candidate to emerge as the GOP standard-bearer.
And McMaster's backing is just the latest in a string of endorsements the Trump campaign has rolled out in the last week.
The campaign first announced former Alaska Gov. Sarah Palin's endorsement
last Tuesday. And this week, the campaign announced endorsements from evangelical leader Jerry Falwell Jr.
, the son of the late influential televangelist, and Sheriff Joe Arpaio
, the hardline Arizona official who gained notoriety for his hardline anti-illegal immigration policies.
As with Palin, whose former aide, Michael Glassner, serves as Trump's political director, Trump is also connected to McMaster through a staff member: Trump's South Carolina political director, Jeff Taillon, who served as McMaster's campaign manager during his successful 2014 bid for lieutenant governor.
South Carolina Gov. Nikki Haley, though, has been critical of Trump's bid, jabbing at the front-runner
in her response to President Barack Obama's State of the Union address earlier this month.
"During anxious times, it can be tempting to follow the siren call of the angriest voices," Haley said. "We must resist that temptation. No one who is willing to work hard, abide by our laws, and love our traditions should ever feel unwelcome in this country."
Haley later confirmed that her remarks were in part aimed at Trump.
Trump, though, has tried to make nice with Haley, calling her a "friend" shortly after she made those remarks.