Credit: Kevork Djansezian/Getty Images

Brie Larson has won the SAG Award for lead actress with her performance as a woman held captive for years with her young son in the harrowing drama Room.

Accepting the prize, Larson thanked costars Jacob Tremblay, Joan Allen, William H. Macy, and the rest of the film’s cast, as well as director Lenny Abrahamson.

“I’m going to write more thank-you cards,” Larson joked. “Okay, bye.”

Portraying Joy, a.k.a. Ma, in the claustrophobic thriller, Larson beat out Cate Blanchett as a sophisticated housewife who romances a shopgirl in Carol, Helen Mirren as a Jewish refugee fighting to recover a stolen Klimt painting in The Woman in Gold, Saoirse Ronan as an Irish immigrant torn between two lives and loves in Brooklyn, and Sarah Silverman as a self-destructive suburban mom in I Smile Back.

The SAG Award is Larson’s first, on her first nomination. She also won the award for lead actress in a drama at the Golden Globes earlier this month, and the two wins give her momentum going into next month’s Oscars.

Speaking to EW recently, Larson said Room had personal resonance for her.

“The story has so much to do with this beautiful allegory with growing up, of being young and living in a small space and seeing things in black and white,” she said. “It takes courage, when the moment happens, to step outside this small space into a world that’s bigger and more complex. That’s exactly what’s happening in my own life.”