Milwaukee, Wisconsin - Donald Trump on Monday named right-wing Ohio Senator J.D. Vance as his running mate in the presidential election, rewarding a one-time harsh critic who became one of his most loyal supporters in Congress.

Trump announced his pick on the first day of the Republican Party convention in Milwaukee, an extravaganza turbocharged by the attempted assassination of the former president.

Seen as the standard-bearer for a new kind of populism that has come to the fore under Trump, 39-year-old Vance embraces the ex-president's isolationist, anti-immigration America First movement.

One of the least experienced VP picks in modern history, the one-term senator is further to the right than the ex-president on many issues including abortion, where he embraces calls for federal legislation.

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He made his name with the 2016 memoir Hillbilly Elegy, a best-selling account of his Appalachian family and modest Rust Belt upbringing, which gave a voice to rural, working-class resentment in left-behind America.

Critics have pointed to numerous awkward remarks one-time "Never Trump guy" Vance has made in the past, including calling the billionaire an "idiot," "noxious," and "reprehensible" as well as suggesting he was "America's Hitler."

Vance reinvented himself as a Trump supporter in recent years and ultimately won the ex-president's key endorsement in the 2022 Ohio Senate race.

Trump could have dropped his big reveal at any point in the days before Milwaukee, but all his pre-convention plans were upended when a gunman made an attempt on his life at a rally in Pennsylvania Saturday.