When A Scott Berg was a 15-year-old high school student, he had three pictures on his bedroom wall at home in Los Angeles.

"F Scott Fitzgerald, my god number one; Woodrow Wilson, our 28th president, god number two; and my third was Don Quixote," reveals the Pulitzer Prize-winning biographer. Strange bedfellows, I suggest to Berg - whose new, exhaustively researched and eloquently written 832-page biography, Wilson, is devoted to one of his great heroes. "Except, except…" responds the ascetically handsome, utterly charming, dapper 63-year-old to my remark. "Here's the link: they are all tragic figures, romantic idealists, who were done in by their own romanticism, and died for a belief in something. So there's the through-line."

Nonetheless, he must surely have been the only kid on the block who had a picture of a long-dead president on his bedroom wall. Fitzgerald, I understand only too well. Quixote? Well, what bookish teenager - especially one who slept with a copy of Fitzgerald's This Side Of Paradise beneath his pillow - hasn't tilted at windmills? But Woodrow Wilson? The simple answer, says Berg, is that Wilson was the architect of much of the last century, re-drawing the map of the world. America's sole president with a PhD, he was known as the scholar president, who also pushed through the most progressive political agenda the nation has ever seen.

"Yet I'd been afraid of writing about him all my life because I held him so high and he was so overwhelming a figure," admits Connecticut-born Berg, when we meet over coffee on a summery London morning (he's in town for the opening of the blockbuster musical, Charlie And The Chocolate Factory, with his film producer partner Kevin McCormick).

The time finally came some 13 years ago. Berg called on his US publishers "with one name I'd been carrying around in my hip pocket for 35 years". When he hesitantly told them he wanted to write about his boyhood hero, they replied, "Go, do it".

It's hardly surprising they would agree to Berg's proposal - he is a best-selling author, who has spent a lifetime writing acclaimed biographies. His first, the brilliant Max Perkins: Editor Of Genius (1978), which won the National Book Award, told of the life and work of the wonderful literary man who edited Fitzgerald, Hemingway and Thomas Wolfe. (It's about to become a Hollywood film, Genius, with Colin Firth as Perkins and Michael Fassbender as Wolfe.)

Berg's other subjects have included Samuel Goldwyn - he received a Guggenheim Fellowship for the Hollywood movie mogul's biography (1989) - the Pulitzer-winning Lindbergh (1998), about the legendary aviator; and Kate Remembered (2003), his memoir of Hollywood actress Katharine Hepburn, his friend of 20 years and the only living subject he's ever tackled. He lived with her for weeks on end, listening to her reminiscences and anecdotes over long fireside chats and glasses of Scotch. As she had wished, the book was not published until after her death.

Between them - Perkins, an east-coast Harvard-educated, ninth-generation American WASP; Goldwyn, an illiterate eastern European Jewish glovemaker, who went to the US west coast and basically invented Hollywood; and Lindbergh, a MidWestener whose life was rich in metaphor and drama - sum up the 20th century. Which was Berg's intention. "I've always wanted to write a shelf full of biographies of 20th century American figures, each from a different wedge of the apple pie. Also, I wanted to write about a Southerner, a political figure, so of course I chose Wilson. Not a lot of people know he was from the South."

Wilson's mother, Jessie, was born in Carlisle, in north-west England, in a house built by Wilson's grandfather - the Reverend Thomas Woodrow, from Paisley - which the president visited. Woodrow Wilson also loved to cycle through Wordsworth's old haunts in the Lake District, according to Berg.

Berg's book reveals how Wilson, a passionate, deeply emotional man, enjoyed the most meteoric rise in American history, before or since. In 1910, he was the president of Princeton, then a small men's college in New Jersey - his (and Berg's) alma mater. In 1912, he won the presidency after being recruited by the Democratic Party to run for governor of New Jersey, albeit briefly.

It is Berg's belief that any president who wants to enact transformative proposals can learn from Wilson, whose biography could not be more timely. Like Barack Obama today, Wilson faced an intransigent Congress, a battle that almost killed him after the First World War, as he fought to create The League of Nations, the first international organisation of countries dedicated to maintaining peace. He always understood, maintains Berg, that sustained dialogue is the best means of finding common ground.

Although whole libraries of books have been devoted to Wilson, Berg had unique access to two caches of papers, letters from Wilson's daughter and his personal physician. "You have no idea what a thrill that was, quite wonderful," he says. (He was also first to open locked-up papers belonging to Goldwyn and Lindbergh, biographical gold dust.)

Nothing, though, has moved Berg as much as the day when, as a young student, he sat in the library at Princeton - he had gone there to walk in the footsteps of F Scott Fitzgerald and Wilson - holding the first draft of The Great Gatsby. Written in pencil on the most fragile paper, "with cross-outs and additions", it's now a relic Princeton keeps locked away.

"It was one of the most magical moments of my life," recalls Berg, who so charmed the librarian in charge of Fitzgerald's archive that she set up the only known recording of the writer speaking into a Record Your Own Voice machine shortly before he died. He recites from - "what else?" - Keats's Ode To A Nightingale. Berg tears up at the memory. "I was just so shaken. I can still remember everything, the sunlight in the room and, of course, his voice. It wasn't deep, it was a little reedy, a little dramatic but quite beautiful. It's what he should have sounded like, unlike Hemingway, who had a very thin, high voice despite the barrel chest."

You could say that Berg imbibed a love of Fitzgerald with his mother's milk. "My mother, Barbara, was reading Fitzgerald in the final pangs of pregnancy so she called me Scott after him - the A is for Andrew. She was reading all the novels and had just read the serialisation of Arthur Mizener's The Far Side Of Paradise, the first big biography of Fitzgerald. She just got swept up in it. This was December 1949, so Fitzgerald was not in fashion. He was dead, buried nine years, so that biography brought him back and that's what really attracted me to biography. You bring lives back."

When he stumbled across Max Perkins's papers - also at Princeton - Berg knew he had found the subject of his senior thesis. "No-one had heard of him, apart from old-timers in publishing. I thought, 'This is a crime.' I was 19, but I knew he would make a great book, so I sort of fell into biography. Perkins was a man who cared so deeply, the warmest, kindest of men. His genius was that he edited by character."

A good man it was a pleasure to live with for a decade? "Oh yes, I always ask myself, 'Do I wish to live with this person for the next 10 or so years?' I remember thinking a few years ago that Hitler deserved a big biography but I could not have woken up with him in my head every morning. Ian Kershaw did it - wonderfully - not me, thank God."

The second of four brothers, Berg was raised in Westport, Connecticut, but when he was seven, the family moved to Los Angeles, where his father, Dick, became a successful TV scriptwriter and film producer. Berg grew up in a house filled with writers and producers. "My parents didn't think actors a healthy influence," he laughs.

Currently, he is a biographer in search of a life. He hasn't chosen the next slice of that apple pie yet. Meanwhile, everyone asks if he has read The Accursed, the latest epic by Joyce Carol Oates. "The world's first post-modern Gothic novel," according to Stephen King, it features Woodrow Wilson, among other real-life figures, as a racist, sexually repressed hypochondriac, addicted to morphine, heroin and opium.

Berg sighs. "Joyce - who is so special, so other-worldly - has Wilson as this raving lunatic, taken over by vampires, who hates women, hates blacks, hates everybody. Of course I haven't read it! I've read about it and that's enough for me." And he points out that he is far from alone in his admiration of Wilson. He was idolised by Roosevelt; Truman called him "the greatest of the greats"; and when Richard Nixon moved into the Oval Office, he requested Wilson's desk for inspiration.

But Berg concludes that Wilson remains one of the most polarising presidents in his nation's history. "Still, he never let go of his vision, his quixotic dreams."

Wilson by A Scott Berg is published by Simon & Schuster, priced £32. His free lecture on Woodrow Wilson, under the auspices of Edinburgh University's School of History, Classics and Archaeology, is at the Meadows Theatre, Teviot Place, Edinburgh, on Thursday. Visit woodrowwilson.eventbrite.co.uk