When JD Vance released his ode to a forgotten Middle America in 2016, he became an instant literary icon.

Hillbilly Elegy, his memoir-come-analysis of the Rust Belt’s decline, and a candid account of the poverty it had wrought, was a cult success which drew on his first-hand experience of violence and addiction.

The timing of the publication was significant. Donald Trump was making his longshot bid for the presidency the same year by tapping into the frustrations of working-class voters who felt left behind by a political elite.

Both understood something many establishment politicians had failed to grasp: America’s working class was ready to leave the Democratic Party behind.

And yet the two men could not have been more different.

Trump, the son of a real estate developer, had enjoyed the high life for decades: gracing the pages of New York’s gossip columns as a firm fixture of the city’s high society.

Mr Vance was born into a far humbler environment in the steel town of Middletown, Ohio, raised in an unstable home by a drug-addicted mother, he leveraged his academic talent into a lucrative career as a lawyer and venture capitalist.

With the platform Hillbilly Elegy had given him, Mr Vance became bracketed with Trump for his ability to tap into the concerns of blue-collar workers in the Rust Belt.

But he made his disdain for the Republican 2016 presidential candidate clear, declaring himself as a “never Trump guy”.

More familiar than most with the scourge of America’s opioid addiction, Mr Vance compared Trump’s candidacy to cultural heroin, branding him “America’s Hitler”.

By the time he was eyeing a political career of his own in 2021, Mr Vance had made a shrewd assessment of the landscape and underwent a conversion to Trumpism.

“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,” he told Fox in 2021.

His newfound fealty secured him the endorsement of the former president in Ohio’s senate race, the most competitive of the 2022 midterms, and with it his US Senate seat.

His fierce support for Trump in Congress, as well as his skill on both cable news and the campaign trail, has now seen him achieve what would have been unthinkable a few short years ago.

As Trump’s 2024 running mate, the 39-year-old could become one of the youngest vice presidents in US history.

Many see opportunism in Mr Vance’s about-face, but friends claim the shift was a reaction to what he viewed as the media’s hysterical response to Trump’s presidency.

“It was a gradual shift that I think was really triggered by the media and the Left’s overreaction to Trump,” one friend told ABC News.

Nevertheless, Mr Vance’s political nous is unmistakable.

He endorsed Trump’s 2024 presidential nomination when many in the GOP cautiously held back - wondering whether Florida governor Ron DeSantis might be a safer bet to win back the White House.

Trump insiders say the 78-year-old, known to place a premium on loyalty, took note of Mr Vance’s early backing.

He was rewarded on Monday when Trump announced: “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 JD Vance.”

Close friend of Donald Jnr

His close friendship with Trump’s eldest son, Donald Jnr, was instrumental to the decision. Don Jnr has long admired Mr Vance’s ability to connect with the Trump base and his skills as a communicator.

Most important of all, according to Trump insiders, is their conviction that Mr Vance’s sincerity will make him a more forceful advocate for their America-first platform.

During his brief tenure in the US Senate, Mr Vance has challenged the legitimacy of the prosecutions against Trump and questioned the results of the 2020 election.

He has also been a vocal critic of US aid to Ukraine and moderated his position on abortion to align with Trump’s more ambiguous rhetoric on the issue.

The Trump campaign believes Mr Vance’s ability to connect with Rust Belt voters, in the all-important swing state of Pennsylvania in particular, will be critical to attracting voters.

His political intelligence has given him a unique ability to connect with both working-class voters, thanks to his blue-collar background, and also highly educated suburban voters who admire his Ivy League pedigree.