Mr Trump has reached the 1,215 delegates needed for the Republican presidential nomination, after contests were held in Georgia, Mississippi, Washington and Hawaii on Tuesday, NBC News is reporting.
Donald Trump has won enough delegates to become the Republican presumptive nominee for a third straight election.
He joins Joe Biden as his party’s presumptive presidential nominee, after he earlier clinched enough delegates to take the Democratic Party’s nomination.
It means the sitting president is expected to face Mr Trump in the election later this year – a re-run of the 2020 vote.
This will be the first time since 1956 that two presidents will go head-to-head.
And the campaign will almost certainly deepen the nation’s political and cultural divides in the eight-month fight for the White House.
Mr Trump won the nomination after contests on Tuesday in Georgia, Hawaii, Mississippi and Washington having already vanquished all his primary opponents.
Former United Nations US ambassador Nikki Haley ended her bid for the Republican nomination last week after winning just one state on Super Tuesday.
Mr Biden too faced little opposition in his primary.
He released a statement after clinching the nomination, in which he said: “Voters now have a choice to make about the future of this country.
“Are we going to stand up and defend our democracy or let others tear it down? Will we restore the right to choose and protect our freedoms or let extremists take them away? Will we finally make the wealthy pay their fair share in taxes – or will we allow corporate greed to run rampant on the backs of the middle class?”
NBC News correspondent Mike Memoli said the result was “not a surprise” given the current president was running against “token opposition” – including Californian Governor Gavin Newsom and Michigan Governor Gretchen Whitmer – who sat out rather than challenge Mr Biden who had already beaten his predecessor once before.
On Monday, before the result, Mr Trump predicted Mr Biden would be the Democratic nominee as he unleashed a new attack on the president’s age.
“I assume he’s going to be the candidate. I’m his only opponent other than life, life itself,” Mr Trump told CNBC.
Mr Biden directed much of his attention toward the former Republican president during a campaign stop in New Hampshire on Monday night.
He described his opponent as a “serious threat to democracy”.
The campaign has not been without difficulties for both frontrunners.
Mr Trump is facing 91 felony counts in four criminal cases involving his handling of classified documents and his attempt to overturn the 2020 election, among other alleged crimes.
He is also facing increasingly pointed questions about his policy plans and relationships with some of the world’s most dangerous dictators.
