Former President Donald Trump on Monday announced Sen. J.D. Vance of Ohio as his vice presidential running mate, as the Republican Party kicked off a national convention to officially crown Trump as the GOP nominee for the November general election.

Trump made the announcement on the 39-year-old critic-turned-supporter in a social media post as GOP delegates and others gathered at the four-day Republican National Convention in Milwaukee, the largest city in the battleground state of Wisconsin.

Vance, a former venture capitalist, is the youngest person to be nominated for vice president since the early 1950s.

"After lengthy deliberation and thought, and considering the tremendous talents of many others, I have decided that the person best suited to assume the position of Vice President of the United States is Senator J.D. Vance of the Great State of Ohio," Trump wrote on Truth Social.

Trump touted the senator's "very successful business career in technology and finance," saying that during the campaign, the running mate will be "strongly focused on the people he fought so brilliantly for -- the American workers and farmers in Pennsylvania, Michigan, Wisconsin, Ohio, Minnesota, and far beyond."

He made the remarks while mentioning Vance's 2016 memoir, "Hillbilly Elegy," -- a book that put him into the national limelight. The book carries his account of growing up in a poor Rust Belt town in a reflection of the struggles facing America's white working class -- a group that helped propel Trump into presidency in 2016.

"J.D.'s book, 'Hillbilly Elegy,' became a major best seller and movie, as it championed the hardworking men and women of our country," Trump wrote.

The former president elaborated on Vance having served in the Marine Corps and graduating from Ohio State University and Yale Law School. At Yale, Vance was an editor of the Yale Law Journal and president of the Yale Law Veterans Association.

The senator has transformed himself from a vocal critic of Trump to a staunch loyalist -- a shift that saw him rising up the political ladder.

He is known to have been closely aligned with Trump's views on election-season issues ranging from immigration to the war in Ukraine. He has also joined the claim that the 2020 election race was "stolen" from Trump.

Trump's choice of Vance appears to reflect his confidence in where his campaign is headed for given that some within the party anticipated that Trump might have to consider a more moderate running mate to help broaden his appeal to voters.

Asked to comment on Vance, President Joe Biden called him a "clone of Trump."

"A clone of Trump on the issues," Biden told reporters on his way to Las Vegas. "I don't see any difference."

In a social media post, Biden wrote that Vance and Trump "want to raise taxes on middle-class families while pushing more tax cuts for the rich."

"Well, I don't intend to let them. And if you're with me, pitch in," he wrote on X, formerly Twitter. (Yonhap)