We Need To Talk About Kevin, a film about a mother's troubled relationship with her son, has won best movie at the BFI London Film Festival awards.
Director Lynne Ramsay said the prize was "light at the end of the tunnel".
Actress Candese Reid won best British newcomer for Junkhearts, Argentine Pablo Giorgelli won best first feature for Las Acacias and Werner Herzog won best documentary for Into the Abyss.
Actor Ralph Fiennes and director David Cronenberg accepted BFI fellowships.
Ramsay's film, starring Ezra Miller as a boy who commits a terrible crime and Tilda Swinton as his mother, is an adaptation of Lionel Shriver's best-selling novel.
"We worked really hard on this one," said Ramsay at the award ceremony at St Luke's church in central London.
"The script was intricate and really well-crafted - we had to do it that way with only 30 days to shoot.
"It's a really major achievement for us, we have been wanting this for years."
Actress Gillian Anderson, a judge for the best film category, said the panel's decision had been tough and that "we did have to battle it out over the table".
We Need To Talk About Kevin beat finalists including Venice film festival winner Faust, Steve McQueen's Shame and The Descendants, starring George Clooney, from Sideways director Alexander Payne.
"One hopes that the winner has an element of the sublime in it that is above and beyond what some of the others have," said Anderson.
"We Need to Talk About Kevin is made with the kind of singular vision that links great directors across all the traditions of cinema," added Shakespeare in Love director John Madden, chair of the judging panel.
Candese Reid won best newcomer for playing a homeless girl, opposite Eddie Marsan, in social British drama Junkhearts. It was her first professional acting role.
Best first feature winner Pablo Giorgelli, who won the equivalent prize at Cannes, said it was "beautiful and strange" just to be invited to London - "that was enough".
His road movie Las Acacias tells the story of a truck driver who picks up a young mother and her baby son.
Herzog's best documentary Into the Abyss: A Tale of Death, A Tale of Life explores the consequences of violence through interviews with Death Row inmates and those close to them.
Fellowship recipients Fiennes and Cronenberg, both had films in the two-week London Film Festival.
Fiennes, star of Schindler's List and The English Patient, had his directorial debut - an adaptation of Shakespeare's Coriolanus - shown at the festival.
Cronenberg's psychoanalysis drama A Dangerous Method, starring Keira Knightley and Michael Fassbender, was also shown.
Canadian Cronenberg, whose works include Eastern Promises and eXistenZ, said that, "especially as you get older, to be acknowledged by your peers, especially in a different country to your own, is really fantastic".
"It really means that your films have a life and a voice aside from you and they've made an impact."
The festival, which has featured more than 300 features and shorts from 55 countries, closes on Thursday with a screening of Terence Davies' adaptation of Terence Rattigan's The Deep Blue Sea, starring Rachel Weisz.