May We Be Forgiven
AM Homes Wins Women's Prize for Fiction with 'Dazzling' Satire
Homes, the fifth American writer in a row to win the £30,000 annual prize, said she was "thrilled" to receive it.
Chair of the judges, actress Miranda Richardson, described the novel as a "dazzling, original, viscerally funny black comedy".
"This is a book we want to read again and give to our friends," she said.
Homes's victory prevented Hilary Mantel's Bring up the Bodies from pulling off an extraordinary triple win.
Mantel's novel, the follow-up to 2009's Wolf Hall, won the Man Booker Prize last year and was named Costa Book of the Year in January.
It had been the odds-on favourite to win the Women's Prize for Fiction - formerly the Orange Prize - which Mantel has never won.
The other novelists on this year's shortlist were Kate Atkinson, Barbara Kingsolver, Maria Semple and Zadie Smith.
Smith won in 2006 with On Beauty, while Kingsolver triumphed in 2010 with The Lacuna.
Homes picked up her prize on Wednesday at an awards ceremony at the Royal Festival Hall in London.
Speaking to BBC Radio Four's Front Row shortly afterwards, she said she had originally conceived her winning novel as a short story.
"I thought it was going to be a short story, but it just kept going - for 700 pages," she told presenter Mark Lawson.
"I allowed myself to go on the ride, which I don't necessarily do. I thought, 'I'm going to write a book I like and entertain myself.'"
Winning the prize, she continued, also allowed her to dispel the air of mystery her use of initials has unwittingly generated.
"For years everyone kept saying, 'Who is AM Homes? Is AM Homes a man or a woman? Or is she trying to hide?'
"Clearly I'm out, I'm a woman and I'm thrilled to win this prize."
May We Be Forgiven focuses on how a shocking act of violence changes the lives of Harry Silver, a historian and Nixon scholar, and his brother George, a high-flying TV executive with a beautiful wife and two children.
"Homes plays with the substance of the American dream, and gives us a horrific, internet-age deconstruction," said Philip Womack in his Daily Telegraph review.
"May We Be Forgiven is a semi-serious, semi-effective, semi-brilliant novel which could not be called, overall, an artistic success," wrote Theo Tate in The Guardian.
"But you'd have to have no sense of the absurd, and no sense of humour, not to be pretty impressed."
Speaking to the BBC, actress Richardson described May We Be Forgiven as a work of "untrammelled imagination".
"It's 21st Century but with ancient themes," she said. "It's not a re-working of anything.
"It's original and viscerally funny and, in the end, irresistible."
The judges' deliberations, which lasted almost four hours on Tuesday night, had been "passionately argued", she said.
Mantel's previous wins for Bring Up The Bodies had not affected the final decision, Richardson added.
"Our concern never can be about what other people think - it's what we think.
"Inevitably, the prize each year is about the individual and collective taste and opinions of whoever the judges are."
Joining Richardson on the judging panel were BBC broadcaster Razia Iqbal, author and editor Rachel Johnson, author JoJo Moyes and Natasha Walter, feminist writer and human rights activist.
"This is the crowning achievement for a fascinating and unpredictable writer, one who fully deserves to be alongside contemporary American greats such as Cormac McCarthy and Richard Ford," said Jonathan Ruppin, web editor for Foyles Bookshop.
"It's a powerful exploration of where the American dream went wrong, laced with sharp observation, pathos and dark humour."
Homes, who lives in New York City, is the the author of two collections of short stories, Things You Should Know and The Safety of Objects.
Her novels include The End of Alice (1996), about an imprisoned paedophile and his correspondence with a teenage girl, and This Book Will Save Your Life (2006), a Los Angeles-set tale about one man's efforts to find redemption.
Her 2007 memoir The Mistress's Daughter told of her adoption and her subsequent reunion with her biological parents when she was in her early thirties.
Homes also wrote and produced for television series The L Word, about the lives of a group of lesbians living in Los Angeles.
Debut US novelist Madeline Miller won the prize last year for The Song of Achilles, a story of same-sex romance set in the Greek age of heroes.
Other previous winners include Lionel Shriver for We Need to Talk about Kevin (2005), Marilynne Robinson for Home (2009) and Tea Obreht for The Tiger's Wife (2011).
Earlier this week the Women's Prize for Fiction announced a new three-year partnership with liqueur brand Baileys.
From 2014, the literary award will be known as the Baileys Women's Prize for Fiction.
The prize this year has been privately supported by companies and individual donors - among them Cherie Blair, entrepreneur Martha Lane Fox and author Joanna Trollope.