The book deals with the story of a dysfunctional family, which is torn by sexual abuse and suicides.
Enright herself has described her book as an intellectual equivalent of a Hollywood weepie and warned that readers looking for a cheery read should not pick it up.
The award's judging panel described The Gathering as a "powerful, uncomfortable and, at times, angry book."
The little-known author's award has come as a shock to India as the country was pinning its hopes on Indra Sinha's Animal People, a novel about the Bhopal gas tragedy. Pakistan-born Mohsin Hamid's The Reluctant Fundamentalist also was a popular choice to win the award.
The Booker Prize, founded in 1969, rewards the best novel of the year written by a writer from Britain, Ireland or a Commonwealth country.
Britain's most prestigious literary award, which includes a cash prize of US$ 1,00,000, was announced at London's medieval Guildhall on Tuesday night.
Image: Anne Enright with her Booker Prize winning novel The Gathering
Photograph: Getty Images