Before the announcement, Enright's fourth novel, The Gathering, had been viewed by many critics as an unlikely candidate for the 50,000 award.
Its themes, after all, are hardly inventive, original or particularly contemporary - the sexual secrets concealed over a couple of generations by a large Irish family that come to a head when one of them commits suicide.
The gathering of the title is that of the 12-strong Hegarty clan for the funeral of Liam, their heavy-drinking brother who was probably - doubts are sown about the episode right at the start - a victim of sexual abuse when he was a child in the mid-1960s.
The story is told by Veronica, who was the nearest in age to Liam, and is now a well-to-do journalist in a disillusioning marriage. Added to her grief at losing her brother is her guilt that she told no-one about a childhood episode in which she saw him being abused by their landlord.
"We found it a very powerful, uncomfortable and, at times, angry book," chairman of the judges Howard Davies said last night. "It is an unflinching look at a grieving family in tough and striking language."
Earlier, many commentators had assumed that the main contest for the prize would be between Ian McEwan's novel On Chesil Beach, which has outsold everything else on the shortlist combined, and Mister Pip, the Commonwealth Prize-winning book by New Zealand writer Lloyd Jones.
Until last weekend, when McEwan drew level on the expectation that he might be the first British writer to win the prize twice, Jones's novel had been the favourite.
Catherine Lockerbie, the director of the Edinburgh International Book Festival, who programmed events with Enright in 2001, 2004 and again this year, said last night: "I'm overjoyed she's won.
"Anne Enright totally deserves to be top of our reading list and now she will be. Her turn of phrase, her eye for detail constantly shift your perspective - and what more can you ask from a writer?"
A LITERARY LANDMARK
SINCE it was founded in 1968 the awarding of the Booker prize, originally called the Booker McConnell and now the Man Booker, is one of the most important events in the publishing year.
Just being included on the shortlist can boost sales, while a win gives an author the honour of being recognised as one of the world's finest writers in the English language.
Past winners include Salman Rushdie, Iris Murdoch, VS Naipaul, Ben Okri and William Golding.