Oscar-nominated Argo is a film based in a time when the Iranian revolution is reaching a boiling point.
The best WGA documentary screenplay award went to Sugar Man, while prizes for work in television were distributed among Breaking Bad (drama series), Louie (comedy series) and Girls (new series).
Aflleck's Iran hostage drama has swept up top prizes at key award shows ahead of Hollywood's top award night, including the Golden Globes, the Screen Actors Guild (SAG), Producers Guild of America (PGA), the Directors Guild of America (DGA), and Britain's BAFTA.
It has won seven Oscar nominations, though not in the best director category, which was perceived as a snub to Affleck.