WASHINGTON - Former US president Donald Trump, the presumptive Republican nominee, received enough delegate votes on Monday to officially become the party's nominee and announced that he has chosen Ohio Senator J.D. Vance as his running mate in the Nov 5 presidential election.

The former president garnered a majority of votes from delegates at the Republican National Convention in Milwaukee, Wisconsin. He reached the required threshold with votes from Florida, which were announced by his son, Eric Trump.

Trump is scheduled to formally accept the party's nomination in a prime-time speech on Thursday. He will lead the Republican Party through a third consecutive election, following his victory against Hillary Clinton in 2016 and his defeat to current President Joe Biden in 2020.

The four-day convention commenced in downtown Milwaukee's Fiserv Forum two days after Trump barely survived an assassination attempt in Pennsylvania and hours after he secured a significant legal victory when a federal judge dismissed one of his criminal prosecutions.

The assassination attempt, which killed one bystander and left Trump with a bloodied ear, immediately shifted the focus of the presidential campaign.

US District Judge Aileen Cannon ruled on Monday to dismiss federal charges against Trump for retaining classified documents after leaving the White House, which effectively removed a major legal threat against the former president, who faces other criminal cases that he says should also be thrown out.

"This dismissal of the lawless indictment in Florida should be just the first step, followed quickly by the dismissal of all the witch hunts," Trump said on Truth Social on Monday, also referring to the prosecution of hundreds of his supporters who stormed the US Capitol on Jan 6, 2021.

Earlier Monday, Trump announced via his social media platform Truth Social that he had chosen Vance as his running mate, ending months of speculation on his vice president pick.

Vance, 39, was elected to the US Senate in 2022 and sworn into office in January 2023. He was a fierce Trump critic in 2016 but has since become a prominent supporter of the former president's "Make America Great Again" agenda, particularly on trade, foreign policy and immigration.

He first achieved recognition with the 2016 memoir "Hillbilly Elegy", a bestseller which detailed his Appalachian family background and Rust Belt upbringing. The book gave a voice to rural, working-class resentment in left-behind America.

Analysts say Vance's selection will boost Trump's support in the Nov 5 election, especially in some Rust Belt states where the election is likely to be decided, but it offers less opportunity to win over more moderate voters and women.

Earlier in the day, Florida Senator Marco Rubio and North Dakota Governor Doug Burgum, the other two finalists, were told they would not be selected.