Ten international judges praised the British-Irish co-production, which drew cheers when it was screened, for “its extraordinary authenticity”.
The award was greeted with strong applause from critics. The jury chairman, the Indian director Mira Nair, said the film captured “the urgency and intention of being part of a historic struggle”.
Bloody Sunday director Paul Greengrass has called it “a bit of warning from history since September 11”, a warning about what could go wrong in so-called wars against terrorism.
The film, which was mostly made with hand-held cameras, with actors improvising dialogue, dramatises events when British paratroops fired on a civil rights march in 1972. Thirteen unarmed people were killed; a 14th man died later.