At age six, Larson was the youngest student admitted to a training program at the American Conservatory Theater, and she began her acting career in 1998 with a comedy sketch on The Tonight Show with Jay Leno.

She subsequently had supporting roles in the comedy films Hoot (2006), Scott Pilgrim vs. the World (2010), and 21 Jump Street (2012), and appeared as a sardonic teenager in the television series United States of Tara (2009–2011).

Her breakthrough came with a leading role in the independent drama Short Term 12 (2013), and she continued to take on supporting parts in the romance The Spectacular Now (2013) and the comedy Trainwreck (2015).

Larson's first major role came as Emily, the younger daughter of Bob Saget's character, in the WB sitcom Raising Dad, which aired for one season during the 2001–02 television schedule.

[29][30] After failing to get cast as Wendy Darling in the 2003 film Peter Pan, Larson wrote and recorded a song titled "Invisible Girl", which received airplay on KIIS-FM.

It received poor reviews, but Ruthe Stein of the San Francisco Chronicle was appreciative of Larson and Linley for bringing "a dash of Indiana Jones to their roles".

[39][40] She had a small part, the following year, in the Amber Heard-starring drama Remember the Daze, and she launched an arts and literature magazine, Bunnies and Traps, for which she wrote her own opinion columns and accepted submissions from other artists and writers.

[43] In 2009, Larson began playing Kate Gregson, the sardonic teenage daughter of Toni Collette's character, coping with her mother's dissociative identity disorder, in the Showtime comedy-drama series United States of Tara.

[44] Reviewing the first season for The New York Times, Alessandra Stanley took note of how well Larson played a "real teenager" and Tim Goodman of the San Francisco Chronicle credited her for finding nuance in her role.

[3][15][29] She featured as a seductive teenager in the critically panned drama The Trouble with Bliss,[62] after which she played Molly, a high school student, in 21 Jump Street, an adaptation of the 1980s police procedural television series, co-starring Jonah Hill and Channing Tatum.

[63] Dana Stevens of Slate labeled Larson "a find of major proportions", adding that "she's not only beautiful but funny, with a scratchy contralto voice, and unlike the usual female in a buddy movie, she comes across as a real person".

[65][66] Following an appearance in the sitcom Community,[67] Larson collaborated with Dustin Bowser to co-write and co-direct Weighting (2013), a short film about a strained relationship, which was screened at South by Southwest.

[59][68] Larson's breakthrough came in the same year when she starred in Destin Daniel Cretton's critically acclaimed independent drama Short Term 12, which marked the first leading role of her career.

[73][74][75] Manohla Dargis of The New York Times found her "terrific" and "completely persuasive", and Ian Freer of Empire stated that she "builds into a whirling dervish of a performance, making Grace strong but scarred, damaged but compassionate".

[78] Larson received a nomination for the Independent Spirit Award for Best Female Lead; she later remarked that the film prompted directors to offer her a wide variety of parts, but she turned down roles of the unidimensional love interest.

[81] The 2014 crime drama The Gambler, based on the 1974 film of the same name, featured Larson as a literature student who has an affair with her professor (played by Mark Wahlberg), a gambling addict.

Filming took place without a script and Larson made several on-set decisions regarding her character's choices, including the removal of a planned romantic subplot involving her and Johnson.

[85][86] Tim Grierson of Screen International labeled the film "a deft blend of laughs, romance and poignancy" and found Larson to be "lively, [but] slightly underused".

[93] Eric Kohn of IndieWire noted how different Larson's role was from that in Room and added that her "businesslike demeanor once again proves her ability to command a scene with a single glare".

[111][112] She was initially skeptical about taking on such a high-profile role, but later accepted the part after viewing it as a platform to empower young women and found a connection with the character's flaws and humanity.

[114][115][116] Stephanie Zacharek of Time wrote that "Larson, a perceptive, low-key actor, carries the whole affair capably" and took note of how much she stood out in the film's quieter moments; David Sims of The Atlantic bemoaned the lack of depth in her role, but credited the actress for effectively portraying her character's struggle for independence from authoritarian men.

[120][121] Also in 2019, Larson teamed with Destin Daniel Cretton for the third time in Just Mercy, based on Bryan Stevenson's memoir about death row inmate Walter McMillian's wrongful conviction, starring Michael B. Jordan and Jamie Foxx.

[124] In 2020, she produced and appeared in an episode of The Messy Truth VR Experience, a virtual reality series created by Van Jones, for which they won the Primetime Emmy Award for Outstanding Original Interactive Program.

[139] Serving as an executive producer, Larson spent two years working on the project, and was pleased by the rare opportunity to prepare for her character while the crew developed the show.

[146] Evening Standard's Tim Bano dismissed the production as an "impenetrable slog", but was appreciative of Larson for "bringing layers of bitterness, resentment and desperation to the lines".

[153] At the following year's ceremony, she presented Casey Affleck with the award for Best Actor, but due to several accusations of sexual harassment made against him, she did not clap for him during a standing ovation from the audience.

[124][179] Describing Larson's off-screen persona, Holly Millea of Elle wrote in 2016 that she "carries herself like an athlete, lean and solid, surefooted [and] yet her energy is warm and familial, literally embracing".

[93][181] Fan Zhong of W magazine has identified a theme of "sex appeal, inner torment, and a quick, playful wit" in her characters, while Allfree believes that she specializes in roles that are "marked by an unmistakable grit".

[189] According to the review aggregator site Rotten Tomatoes, Larson's most critically acclaimed films include Scott Pilgrim vs. the World (2010), 21 Jump Street (2012), Short Term 12 (2013), Don Jon (2013), The Spectacular Now (2013), Trainwreck (2015), Room (2015), Kong: Skull Island (2017), Captain Marvel (2019), and Avengers: Endgame (2019).

[191][192][193][194] She also won the Primetime Emmy Award for Outstanding Original Interactive Program for producing the virtual reality series The Messy Truth VR Experience (2020).