The victory is the second for the film since its premiere earlier this month at the Venice film festival, where it received the best screenplay prize.
Martin McDonagh’s black comedy Three Billboards Outside Ebbing, Missouri has received a major boost in its Oscar prospects by winning the top honour at the Toronto international film festival.
Other winners at the festival included battle-rap drama Bodied, which won the People’s Choice Midnight Madness award for genre, shock and cult cinema, and photographer Agnès Varda’s Visages, Villages, which won the People’s Choice prize for best documentary.
The Platform prize for international film, meanwhile, was won by Warwick Thornton’s Sweet Country, a period western set in Australia’s Northern Territory.