Just a day after picking up the Outstanding Directorial Achievement in a Feature Film prize at the Directors Guild of America Awards in Hollywood, Affleck's drama bagged the top honour from the UK Regional Critics' Film Awards.
In a statement, the star offered his thanks "on behalf of all the cast and production team".
Sam Mendes' work on James Bond epic Skyfall landed him the director of the year title, while Ben Whishaw was named rising star for his role in the blockbuster.
Robert Pattinson was honoured with the best British performance award for his work on The Twilight Saga: Breaking Dawn - Part 2 after a public vote, while dark comedy Sightseers was named screenplay of the year.
The UK Regional Critics' Film Awards are dedicated to actor Richard Attenborough and are voted for by journalists and bloggers who write or broadcast for local media throughout Britain.