Trump VP pick: Former president announces Vance as his running mate

Former President Donald Trump has picked Ohio Sen. J.D. Vance as his running mate, placing a young, ideological ally alongside him on the Republican 2024 ticket.

Trump announced Vance would be his running mate on Monday, writing on Truth Social that the Ohio Republican is "the person best suited to assume the position of Vice President of the United States."

The decision caps off months of speculation and sees Trump elevate a 39-year-old first-term senator whose roughly year and a half tenure in the Senate has seen him emerge as a staunch ideological ally of the former president.

"As Vice President, J.D. will continue to fight for our Constitution, stand with our Troops, and will do everything he can to help me MAKE AMERICA GREAT AGAIN," Trump posted on Truth Social.

The Trump campaign wasted no time promoting the former president's pick, posting an ad on social media featuring a montage of Vance praising Trump.

"I am proud that I have been an ally of Donald Trump's in Washington, D.C.," Vance says in one of the clips in the ad.

The campaign is also fundraising off of the announcement, saying he "always knew" he "needed" Vance on his side.

President Joe Biden's campaign released a statement on Vance being named Trump's vice presidential pick, slamming Vance as someone who will further Trump's "extreme MAGA agenda."

"Donald Trump picked J.D. Vance as his running mate because Vance will do what Mike Pence wouldn't on January 6: bend over backwards to enable Trump and his extreme MAGA agenda, even if it means breaking the law and no matter the harm to the American people," Biden Campaign Chair Jen O'Malley Dillon wrote in a statement.

MORE: Who Is JD Vance? From 'never-Trump guy' to his VP pick

Vance rose to fame through his 2016 book, "Hillbilly Elegy." He evolved from a "never-Trump guy" to one of Trump's strongest surrogates in an eight-year span.

Vance was born in Middleton, Ohio, and served in the Marine Corps. He later attended Ohio State University and eventually graduated from Yale Law School.

He was a corporate lawyer and then worked in the tech industry as a venture capitalist.

In 2016, Vance released his memoir, "Hillbilly Elegy," which shared his story of growing up in poverty in America's Rust Belt and being surrounded by violence and addiction.

Vance eventually became an emissary between the media and those in the Rust Belt during the 2016 election, discussing the issues important to those who had a similar background to him.

During this time, Vance made his disdain for Trump clear, saying he was a "never-Trump guy" in an interview with Charlie Rose in 2016.

In August 2016, he told ABC News that he didn't see Trump "offering many solutions."

But Vance would eventually align with the former president, praising his time in office and apologizing for his attacks on him during an interview with Fox News in July 2021.

"I've been very open about the fact that I did say those critical things, and I regret them, and I regret being wrong about the guy," Vance said on Fox News in 2021.

His apology came around the same time Vance entered the race for the open Ohio Senate seat, which became one of the most competitive GOP primaries of the 2022 election cycle. Trump endorsed Vance for the job, which helped him win both the primary election and general election against Ohio Democrat Tim Scott.

RELATED: 'You can help me win': How Trump landed on JD Vance as his VP pick

In his role as senator, some of his most notable work has been responding to the East Palestine train derailment in his home state. He has also stayed true to his tough conservative brand, including opposing aid to Ukraine.

In 2024, Vance has been a reliable surrogate for Trump -- appearing at campaign events, defending him in television appearances and helping the former president raise money for his campaign.

ABC News' Soorin Kim, Lalee Ibssa, Kelsey Walsh and Sarah Beth Hensley contributed to this report.