Donald Trump has reached the number of delegates needed to win the Republican nomination for president, according to an Associated Press news agency count.
The real estate billionaire was one delegate over the 1,237 threshold on Thursday after a small number of unbound Republican delegates said they would back him.
With another 303 delegates at stake in five state primaries on 7 June, Mr Trump is expected to easily increase his total and avoid a contested party convention in Cleveland, Ohio, in July.
Against all expectations, the political newcomer saw off 16 other Republicans who sought the party’s presidential nomination for November’s election.
Former US Secretary of State Hillary Clinton, who looks likely to be Mr Trump’s Democratic opponent, is close to securing the delegate numbers she needs to win her party’s nomination.
Steve House, chairman of the Colorado Republican Party and an unbound delegate, said he liked Mr Trump’s background as a businessman.
He said: “Leadership is leadership. If he can surround himself with the political talent, I think he will be fine.”
Oklahoma Republican chairwoman Pam Pollard added: “I think he has touched a part of our electorate that doesn’t like where our country is.
“I have no problem supporting Mr Trump.”
Republican officials have been wary of Mr Trump’s caustic style and provocative statements on Mexicans, women, building a wall between the US and Mexico and banning Muslims from the US.
But millions of grassroots activists, many of them outsiders to the political process, have praised what they see as his truth-telling.
Mr Trump spent just $57m (£39m) on his campaign through the end of April.
He covered most of that with at least $43m of his own money loaned to the campaign.
He also spent less than $21m on paid TV and radio commercials – around a quarter of the amount spent by Florida Governor Jeb Bush, who dropped out of the race three months ago.
Mr Trump became the presumptive nominee earlier this month after Texas Senator Ted Cruz and Ohio Governor John Kasich dropped out of the race.
But securing the necessary delegates effectively ends his primary campaign.