Argo and Zero Dark Thirty have won the top honours from the Writers Guild of America.
Ben Affleck’s Iran hostage drama Argo, written by Chris Terrio, won for adapted screenplay.
Zero Dark Thirty, Kathryn Bigelow’s film about the hunt for Osama Bin Laden, written by Mark Boal, won best original screenplay.
The award is the latest accolade for Argo, which has won at the Baftas and the Golden Globes, as well as gongs at the Directors Guild of America, the Screen Actors Guild and the Producers Guild of America.
The film looks most likely to win against favourite Lincoln at this Sunday's Academy Awards.
Last year adapted screenplay winner The Descendants and original screenplay winner Midnight in Paris went on to win Oscars in the same category.
At last night's Writers Guild Award Malik Bendjelloul won best documentary screenplay for the film Searching for Sugar Man, about the rediscovery of the musician Rodriguez.
Breaking Bad won for televised drama series and Lena Dunham’s Girls took home the prize for new TV series.
Director and writer Nora Ephron, who died in June last year, was given a special tribute during the ceremony.