The film also beat out nominees "127 Hours," "Black Swan," "Inception," "The Fighter," "The Kids Are All Right," "The Town," "Toy Story 3," and "True Grit."
The PGA awards, hosted by filmmaker Judd Apatow at the Beverly Hilton, are part of the steady stream of ceremonies leading up to the Academy Awards.
"The Social Network," which stars Jesse Eisenberg as Facebook founder Mark Zuckerberg, appeared to be on the fast track to a best picture Oscar after dominating honors from top critics groups and winning the Golden Globe last week.
But Saturday's win solidified a spot as an Academy Award contender for "The King's Speech," which features Golden Globe best actor winner Colin Firth playing Queen Elizabeth II's father, George VI, as he tries to overcome a debilitating stammer.
The Producers Guild followed the lead of the Oscars last year and doubled its best-picture field to 10 movies.
In other PGA categories, Pixar's "Toy Story 3" won for best animated feature and the chronicle of modern education "Waiting for Superman" took top documentary honors.
On the television side, AMC's "Mad Men" won for best drama series for the third straight year, and ABC's "Modern Family" won best comedy, beating out previous two-time winner "30 Rock."
HBO's "The Pacific" won for best TV movie or miniseries, and Comedy Central's "The Colbert Report" won for top live entertainment or reality show.