Sag's lead-acting honours went to Jennifer Lawrence for her role as a troubled widow in a shaky new relationship in the lost-souls romance Silver Linings Playbook and Daniel Day-Lewis as Abraham Lincoln in the Civil War epic Lincoln. Anne Hathaway of Les Miserables and Tommy Lee Jones of Lincoln won the supporting-acting honours.
"It occurred to me — it was an actor that murdered Abraham Lincoln," said Day-Lewis, a solid front-runner to join an exclusive list of three-time acting Oscar winners. It was a brisk, businesslike and fairly bland evening as the actors union handed out honours to a predictable line-up of winners who generally had triumphed at earlier Hollywood ceremonies or past SAG shows.
The SAG cast win came a day after Argo claimed the top honour from the Producers Guild of America, whose winner often goes on to claim best picture at the Academy Awards.
Argo also was a surprise victor two weeks ago at the Golden Globes, where it won best drama and director for Ben Affleck.
The awards momentum positions Argo for a rare feat at the February 24 Oscars, where it could become just the fourth film in 85 years to be named best picture without a nomination for its director.
"To me this has nothing to do with me, it has to do with the incredible people who were in this movie," said Affleck, who also stars in Argo and accepted the SAG prize alongside his cast.
Affleck plays CIA agent Tony Mendez, who masterminded the daring rescue of six US embassy workers in Iran after the 1979 hostage crisis erupted. A directing nomination at the Oscars usually goes hand in hand with a best-picture win.
When Affleck was snubbed for a directing slot, awards analysts initially were counting Argo out for the best-picture Oscar, along with Kathryn Bigelow's Zero Dark Thirty and Tom Hooper's Les Miserables, which also missed out on directing nominations.
Only once in modern times has a film won best picture without a directing nomination, with 1989's Driving Miss Daisy. The other two times came in the show's early years, at the first Oscars in 1929 with Wings and for 1932's Grand Hotel.
But Argo has proven a resilient crowd-pleaser, dominating at awards shows since then over Steven Spielberg's Lincoln, which leads the Oscars with 12 nominations. The cast prize at SAG adds some weight to the Oscar prospects for Argo, though the guild honour has a spotty record at forecasting eventual best-picture winners.
Only eight of 17 times since the guild added the category has the cast winner gone on to take the best-picture Oscar. The Help won the guild's cast prize last year, while Oscar voters named The Artist as best picture.
The acting prizes solidify those categories, though. Silver Linings star Lawrence won a Golden Globe and has become one of Hollywood's hottest talents, with part two of her blockbuster franchise, The Hunger Games: Catching Fire, due out in November.
"Now I have this naked statue that means some of you even voted for me, and that is an indescribable feeling," Lawrence said after explaining she earned her SAG card aged 14 by filming a spot for MTV.
Hathaway won for her role as a doomed single mother forced into prostitution in the adaptation of the stage musical based on Victor Hugo's epic novel. Her win came over four past Oscar recipients — Sally Field, Helen Hunt, Nicole Kidman and Maggie Smith.
"I'm just thrilled I have dental," Hathaway said. "I got my SAG card when I was 14. It felt like the beginning of the world. I have loved every single minute of my life as an actor. Thank you for nominating me alongside incredible women and incredible performances."
Jones, who was not at the show, won for his turn as abolitionist firebrand Thaddeus Stevens in the Civil War epic. Day-Lewis, a two-time Oscar winner for My Left Foot and There Will Be Blood, could become the fifth actor to earn three Oscars, along with Meryl Streep, Jack Nicholson, Ingrid Bergman and Walter Brennan. Katharine Hepburn has the acting record with four Oscars.
On SAG's television side, with 30 Rock ending its run, its stars Tina Fey and Alec Baldwin won the SAG awards for best comedy performers. It was Baldwin's seventh-straight win, while Fey earned her fifth SAG prize.
The TV drama acting awards went to Claire Danes of Homeland and Bryan Cranston of Breaking Bad. Downton Abbey won the TV drama cast award. Julianne Moore's turn as Sarah Palin in Game Change earned her the TV prize for best actress in a movie or miniseries. Kevin Costner won for best actor in a movie or miniseries for Hatfields & McCoys.