Jon Favreau was barely out of college when he met Barack Obama. The then Illinois senator was pacing backstage at the 2004 Democratic Convention, rehearsing the lines of a speech that would catapult him on to the national stage.

Mr Favreau listened to Mr Obama’s resonant tones, and then he interrupted: could the senator rewrite that line to avoid an overlap? “He looked at me, kind of confused,” Mr Favreau later recalled. “Like, who is this kid?”

At 27, by the standards of the West Wing, the crop-haired, baby-faced Mr Favreau is still a kid. But the West Wing is where he will report for work come Inauguration Day. This week Mr Obama confirmed that his wunderkind wordsmith would be moving to the White House with him as the youngest head of a presidential speechwriting team so far.

It is an extraordinary ascent for the Catholic-college graduate who began as a grunt on John Kerry’s presidential campaign and fell into speechwriting by accident as the 2004 Democratic campaign imploded. Staffers abandoned the presidential hopeful in droves as it seemed Mr Kerry would lose the primaries to Howard Dean. “They couldn’t afford to hire a speechwriter,” Mr Favreau said years later. “And they couldn’t find anyone who wanted to come in when we were about to lose to Dean. So I became deputy speechwriter even though I had no previous experience.”

Mr Favreau’s fledgeling talent may have failed to make Mr Kerry’s rhetoric soar, but he had caught the eye of the Obama team. Mr Favreau took some convincing. “After all the backbiting and nastiness, my idealism and enthusiasm for politics was crushed,” he said. But he was out of a job, “broke, taking advantage of all the happy hours I could find in Washington”, as he told The New York Times, so agreed to be interviewed for the job.

The two met and hit it off immediately. Since then, only a handful of people have spent more time with Mr Obama than his youthful scribe. The pair spent hours “just hanging out”, watching baseball and talking politics.

Mr Favreau describes the process as something like ghostwriting, absorbing Mr Obama’s cadences until they became his own. As Mr Obama’s schedule became increasingly fraught he was forced to lean on his speechwriter more and more, a difficult leap of faith for a bestselling author in his own right. But as Mr Favreau has said, being Mr Obama’s speechwriter is like being “Ted Williams’s batting coach”, evoking the most gifted hitter in baseball history.

“What I do is sit with him for half an hour,” Mr Favreau said. “He talks and I type everything he says.” As he does so, “his voice is always in my head when I’m writing, just to make sure that it jives with what he wants to say. . . I reshape it. I write. He writes. He reshapes it. That’s how we get a finished product.”

The result is such memorable lines as “They said this day would never come”, and the iconic slogan: “Yes we can.”

On the day before the election, Mr Favreau was told: “Figure out a good Lincoln quote to bring it all together.”

Mr Favreau skipped Lincoln’s most oft-quoted phrase – “the better angels of our nature” – to choose a lesser-known passage. “We are not enemies, but friends . . . Though passion may have strained, it must not break our bonds of affection.”

Mr Favreau’s youth, boyish good looks and evident brilliance are winning him a following in his own right. “Jon Favreau is my future husband, he just doesn’t know it yet,” one smitten blogger wrote beneath a web profile.

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