George Saunders has won the Man Booker prize for his novel Lincoln in the Bardo - becoming the second US author to take home the £50,000 fiction award.
The book tells the story of Abraham Lincoln's grief after the death of his young son, and his visits to his tomb.
It is the first full-length novel from Saunders, previously best known for his short stories, and is set in a graveyard, over a single night.
Judges praised the "utterly original" work and said it was "deeply moving".
Saunders, 58, was one of six authors shortlisted for the prestigious award, alongside British writers Ali Smith and Fiona Mozley, fellow Americans Paul Auster and Emily Fridlund, and British-Pakistani author Mohsin Hamid.
Speaking after his name was announced, Saunders said: "Thank you for this great honour which I hope to live up to with the rest of my work, for the rest of my life."
The Texas-born author, who lives in New York, has previously won the Folio Prize and Story Prize for his short story collection Tenth of December. Lincoln in the Bardo is his ninth book, and had been the favourite to win the Booker.
He based the story on a real moment in 1862 when the body of the US president's 11-year-old son Willie was taken to a cemetery in Washington DC.
Saunders revealed after writing the first third of the book he "got a bit freaked out" and wasn't sure "if any other human being could read it".
His wife Paula then read it and wrote on a post-it note "something so generous it will stay a secret forever" and that gave him the confidence to continue.
During a post-ceremony press conference, he said: "It sounds a little pathetic but for an artist I think validation is really helpful. Maybe you shouldn't need it but I definitely do.
"So when someone that I respect approves my work or when I get grouped with a bunch of writers like these wonderful talents, my opinion of myself improves a little bit and the next book has a little more courage in it."
Saunders said the novel had been in his heart for 20 years before he wrote it.
Asked why it took him so long to commit it to the page, he told the BBC: "My stories are a little dark and cynical and sci-fi, and I just couldn't see any way to approach this serious material.
"I tried a couple of times and it didn't work, and I just thought: 'Either don't do it, or wait until you've enough life to do it justice'."
Baroness Lola Young, chair of the 2017 judging panel, said the form of the novel - which includes voices of 166 souls in the graveyard - "reveals a witty, intelligent and deeply moving narrative".
It took five hours of deliberations before the panel, also including novelist Sarah Hall, artist Tom Phillips, literary critic Lila Azam Zanganeh and the travel writer Colin Thubron, made their unanimous decision.
Baroness Young described the responsibility of choosing a winner as "draining", saying: "We had actually some tears - but that was as much due to the kind of relief of having gotten to the decision, it wasn't about anger or sadness or whatever."
She added: "This really stood out because of its innovation - its very different styling and the way in which it paradoxically brought to life these not-quite-dead souls in this other world.
"There was this juxtaposition of the very personal tragedy of Abraham Lincoln with his public life, as the person who'd really instigated the American Civil War."