Trump's eldest child, Donald Trump Jr, announced the support of New York, their home state, during a roll-call vote at the Republican National Convention, ensuring Trump had the majority of delegates - 1,237 - needed to contest the November 8 US presidential election against presumptive Democratic nominee Hillary Clinton.
Trump's son said: "It is my honor to be able to throw Donald Trump over the top in the delegate count tonight."
"Congratulations, Dad. We love you," Trump Jr said.
Trump's Democratic rival, Hillary Clinton tweeted after the vote: "Donald Trump just became the Republican nominee. Chip in now to make sure he never steps foot in the Oval Office."
Trump won the nomination with 1,725 delegates, followed by US Senator Ted Cruz of Texas with 475 delegates, Ohio governor John Kasich with 120 and US senator Marco Rubio of Florida with 114. Three other candidates emerged with a total of 12 delegates.