Mulligan made her professional acting debut on stage in Kevin Elyot's play Forty Winks (2004) at the Royal Court Theatre.

Her career progressed with roles in Never Let Me Go (2010), Drive (2011), Shame (2011), Inside Llewyn Davis (2013), Far from the Madding Crowd (2015), Suffragette (2015), Mudbound (2017), Wildlife (2018), and She Said (2022), and she had her highest-grossing release in the period drama The Great Gatsby (2013).

She received further Academy Award nominations for her portrayals of a vigilante in the black comedy Promising Young Woman (2020) and Felicia Montealegre in the biopic Maestro (2023).

Several weeks later, Fellowes's wife Emma invited Mulligan to a dinner she and her husband were hosting for young aspiring actors.

[10][6][13][14] During her late teens and early twenties, she worked as a pub barmaid and an errand-runner for Ealing Studios between acting jobs.

Later that year, she won the role of orphan Ada Clare in the BAFTA award-winning BBC adaption of Charles Dickens' Bleak House, her television debut.

[19] She rounded out 2007 by appearing in an acclaimed stage revival of The Seagull, in which she played Nina alongside Kristin Scott Thomas and Chiwetel Ejiofor.

[21] For her debut Broadway performance in the 2008 American transfer of The Seagull, she was nominated for a Drama Desk Award, but lost to Angela Lansbury for Blithe Spirit.

[22] Her breakthrough came when, at 24, she was cast in her first leading role as Jenny, a teenage school girl seduced by an older man in the 2009 independent coming of age film An Education.

[25][26] Rolling Stone's Peter Travers described her as having given a "sensational, starmaking performance,"[27] Mulligan received a nomination for the BAFTA Rising Star Award, which is voted on by the British public.

[28] In 2010, she was invited to join the Academy of Motion Picture Arts and Sciences,[29] That same year she starred in the film adaptation of Kazuo Ishiguro's acclaimed novel Never Let Me Go with Keira Knightley, and Andrew Garfield.

[32] She returned to the stage in the Atlantic Theater Company's off-Broadway play adaptation of Ingmar Bergman's Through a Glass, Darkly, from 13 May – 3 July 2011.

[34] Ben Brantley, theater critic for The New York Times, wrote that Mulligan's performance was "acting of the highest order"; he also described her as "extraordinary" and "one of the finest actresses of her generation.

Todd McCarthy of The Hollywood Reporter wrote of her performance, "Exposing herself emotionally and physically as she never has before, Mulligan is terrific in this unexpected role of a deeply wounded and troubled soul.

While attending a Vogue fashion dinner in New York City in November, Baz Luhrmann’s wife, Catherine Martin, told her she had the part.

[41][42] In 2013, she also starred in Joel and Ethan Coen's black comedy Inside Llewyn Davis alongside Oscar Isaac, and Justin Timberlake.

The transfer was a massive success with Marilyn Stasio of Variety declaring that the two central performances left the audience "breathless — and wondering how they can sustain this level of emotional intensity throughout the show’s 13-week Broadway run.

[50][51] In 2015, Mulligan starred in Thomas Vinterberg's film adaptation of Thomas Hardy's novel Far from the Madding Crowd with Matthias Schoenaerts, Tom Sturridge, and Michael Sheen,[52][53] Anne Thompson of IndieWire wrote that her performance "proves that she can carry a movie" adding, "Carey Mulligan is excellent: her face has a pinched girlish prettiness combined with a shrewd, slightly schoolmistressy intelligence".

[54] In the fall of that year she starred in Sarah Gavron's Suffragette (2015) with Helena Bonham Carter, Ben Whishaw, Brendan Gleeson and Meryl Streep.

On review aggregator Rotten Tomatoes, the film has an approval rating of 97% with the consensus reading, "Mudbound offers a well-acted, finely detailed snapshot of American history whose scenes of rural class struggle resonate far beyond their period setting.

The film has earned a 94% on Rotten Tomatoes with the consensus reading, "Wildlife's portrait of a family in crisis is beautifully composed by director Paul Dano – and brought brilliantly to life by a career-best performance from Carey Mulligan.

Mulligan stepped back into television as a Detective Inspector in Collateral, a BBC Two limited series, receiving plaudits from American and British critics.

[62] In 2020, Mulligan starred in Emerald Fennell's black comedy thriller film Promising Young Woman, alongside Bo Burnham and Alison Brie.

The website Rotten Tomatoes lists the film's rating as 90%, with a critics consensus reading, "A boldly provocative, timely thriller, Promising Young Woman is an auspicious feature debut for writer-director Emerald Fennell — and a career highlight for Carey Mulligan.

[65][66] In 2021, Mulligan replaced Nicole Kidman in The Dig, a film about the events of the 1939 excavation of Sutton Hoo, co-starring Ralph Fiennes and Lily James.

She portrayed Megan Twohey, one of the real life New York Times reporters who broke the Harvey Weinstein scandal.

[83] Aside from acting, Mulligan was among the actresses who took part in the Safe Project—each was photographed in the place she feels safest—for a 2010 series to raise awareness of sex trafficking.