The Oscar-winning actress stars as a mother coming to terms with the fact her son, Kevin, has committed mass murder at his high school.
The film, based on Lionel Shriver's 2003 novel of the same name, saw off competition from George Clooney's latest offering, The Descendants, to win the coveted Best Picture at the British Film Institute's (BFI) movie event on Wednesday night (26Oct11).
Judging panel chairman John Madden says, ""In the end, we were simply bowled over by one film - a sublime, uncompromising tale of the torment that can stand in the place of love. We Need To Talk About Kevin is made with the kind of singular vision that links great directors across all the traditions of cinema.""
Actress Candese Reid won the British Newcomer award for her movie debut in Junkhearts, while Argentinian director Pablo Giorgelli scooped The Sutherland Award for Las Acacias.
Canadian director David Cronenberg and British actor Ralph Fiennes were awarded the festival's highest accolade, the BFI Fellowship.