Backstage, Spencer called the win "beyond profound," and Davis said she's proud to have worked on a film that tells stories that aren't often front and center.
"They are the stories of our mothers, our grandmothers, and we absolutely feel like these women's stories are worth it," Davis said.
"The Help" also claimed the guild's ensemble award, the show's equivalent of a best-picture prize.
For "The Artist," Jean Dujardin won the lead-actor honor as a silent-film superstar whose career crumbles when the sound era arrives.
Christopher Plummer, 82, won for supporting actor as an elderly dad who comes out as gay in "Beginners"
On the TV side, "Modern Family" won its second straight SAG Award for best ensemble cast in a comedy series.
"Boardwalk Empire" took the prize in the dramatic category.
Mary Tyler Moore received the Screen Actors Guild Life Achievement Award.