A small group of Republican delegates declared for Trump on Thursday, putting him above the 1,237 votes he needed to ensure the party nomination.
Trump has been the only Republican candidate since his final two rivals, Ted Cruz and John Kasich, bowed out of the race earlier this month. By topping the minimal delegate count, however, Trump is set to avoid a contested party convention in July, thus clearing the final hurdle towards the nomination.
Republican delegate from Oklahoma, Pam Pollard, said that Trump had "touched a part of our electorate that doesn't like where our country is."
"I have no problem supporting Mr. Trump," she said.
Other candidates told AP they would back Trump out of sense of obligation because he won primary ballots in their home states.
Cameron Linton of Pittsburgh, Pennsylvania, said he will back Trump on the first convention ballot since he won the presidential primary in his district.
"If there's a second ballot I won't vote for Donald Trump," Linton said. "He's ridiculous. There's no other way to say it."
Sanders, Trump hint at debate
Trump started his campaign in June 2015, with his firebrand style and controversial statements drawing attention in the crowded field he shared with 16 other candidates. He is now set to face off against the Democratic nominee in the November general election.
Two candidates are still competing for the Democratic nomination, with former US Secretary of State Hillary Clinton leading the delegate count over Vermont Senator Bernie Sanders. The rivals have been bumping heads during the race, with Clinton recently refusing to debate Sanders ahead of the upcoming California primary.
On Wednesday, Trump said he would be willing to debate the leftist senator.
"If I debated him, we would have such high ratings," Trump said appearing on ABC's "Jimmy Kimmel Live."
Sanders responded to the statement on Twitter.
However, Trump campaign spokesman Hope Hicks said on Thursday there were no formal plans for the event.
A number of recent polls have shown Sanders as the winner of a potential match-up against Trump in the general ballot.