"I'm completely over the moon and speechless," Larson said by phone Thursday after pausing the Netflix series "Making a Murderer" to watch the Oscar nominations live-stream online.
Oscars 2016: Full Coverage | Complete list | Snubs, surprises and reactions | Top nominee photos | Oscars are so white, again
Larson's lead performance as Ma, a young mother living in captivity, first drew praise for its power and sensitivity at the Telluride Film Festival in September and has steadily collected accolades all season long — on Sunday she won a
An independent drama based on an intense, bestselling 2010 novel by Emma Donoghue,
"It's been this sort of snowball, which is picking up momentum," Larson said of the movie's critical success. "I'm so moved by it. Seeing Lenny's nomination is a really big surprise and so exciting and well deserved. It all started with Emma Donoguhe."
Although many moviegoers may be learning her name for the first time, Larson has been a working performer since she was a child, appearing first in commercials and TV shows and releasing a pop music album at age 16.
Like many younger actors, Larson toggles between smaller indie fare like "Room" and bigger mainstream movies. After a breakthrough performance in the 2013 independent film "Short Term 12," she has been making more studio films, playing Amy Schumer's little sister in last summer's comedy "Trainwreck," and getting cast in "Kong: Skull Island," due next March.
In "Room," Larson spends much of the film alone in scenes with Jacob Tremblay, now 9, who plays her son born of rape and raised in captivity. In preparation for the role, Larson interviewed victims of sexual abuse and spoke with a trauma counselor and also reflected on sacrifices her own mother made after her parents' divorce.
Promoting the film has been a much lighter endeavor, involving parties, red carpets, high fashion and meeting her Hollywood peers. Larson's glamorous metallic gown at Sunday's Golden Globes ceremony was an indicator of her rising stature in the industry.
After a party in Telluride where the academy gave away T-shirts with Oscars on them, Larson joked about wearing the shirt while doing press but said at the time, "I don't know if people will get that I'm being funny."
"The part that's been so exciting has been the human connection part," Larson said on Thursday. "It's been a lot of celebration with people that I love. It feels so good to be able to clink Champagne glasses with people. It's really important to be able to hug others."