Mara had a career breakthrough when she starred as Lisbeth Salander in Fincher's thriller The Girl with the Dragon Tattoo (2011), which earned her a nomination for the Academy Award for Best Actress.

Mara's career progressed with leading roles in the thriller Side Effects (2013), the science fiction romance Her (2013), and the romantic drama Carol (2015).

Mara is known for her charity work and oversees the Uweza Foundation, which supports empowerment programs for children and families in the Kibera slum of Nairobi.

Her father, Timothy Christopher Mara, is the senior vice president of player personnel for the New York Giants; and her mother, Kathleen McNulty (née Rooney), is a part-time real estate agent.

[16] Mara was inspired to act by seeing musical theatre and classic movies, like Gone with the Wind (1939), Rebecca (1940), and Bringing Up Baby (1938), with her mother.

She found work in television, making her professional debut in a 2006 episode of the drama Law & Order: Special Victims Unit, as a girl who bullies overweight children.

In a coming-of-age film Tanner Hall (2009), Mara landed her first lead role, as Fernanda who has an affair with a married family friend (Tom Everett Scott).

[25] In Miguel Arteta's comedy-drama film Youth in Revolt, Mara played Taggarty who tries to sleep with fifty men before she goes to college.

[28] Mara played Courtney in the 2009 independent film Dare[29] and in The Winning Season as Wendy, a high school basketball player having an affair with a middle-aged shoe salesman (Kevin Breznahan) with a similar story to The Bad News Bears.

[17] Mara starred in a remake of the 1984 horror film A Nightmare on Elm Street,[31] as the protagonist Nancy Holbrook, a high school student victimized by Freddy Krueger (Jackie Earle Haley).

[6] Mara appeared at the Hamptons International Film Festival in October 2009 as part of its Breakthrough Performers Program, where she was tutored by Sharon Stone.

[35] In 2010, Mara played Erica Albright, Mark Zuckerberg's ex-girlfriend, in David Fincher's biographical drama film The Social Network.

[36] The same year, Mara was cast as the lead in a film adaptation of The Girl with the Dragon Tattoo, the first of the Millennium book trilogy by Stieg Larsson.

She played Lisbeth Salander, a brilliant but troubled computer hacker who helps journalist Mikael Blomkvist (Daniel Craig) solve a series of murders.

[44] Mara's long brown hair was cut short and dyed black, in a style reminiscent of 1970s punk and 1980s goth fashions.

[50][51] The following year, Mara signed on to replace Carey Mulligan, who had to drop out due to scheduling conflicts, in Spike Jonze's Her (2013), where she played Catherine Klausen, the ex-wife of central character Theodore Twombley (Joaquin Phoenix).

[52][53] In addition, Mara starred in Steven Soderbergh's psychological thriller Side Effects (2013), replacing Blake Lively.

She played Emily Taylor, "a woman who turns to prescription medication as a way of handling her anxiety concerning her husband's upcoming release from prison.

"[55] She also starred in David Lowery's romantic crime drama Ain't Them Bodies Saints (2013), which was described as a modern-day Bonnie and Clyde story, alongside Casey Affleck and Ben Foster.

[57] Mara's sole release of 2014 was the crime drama thriller film Trash, an adaptation of the 2010 novel of the same name by Andy Mulligan directed by Stephen Daldry.

[58] In 2015, Mara starred opposite Cate Blanchett in Todd Haynes's highly acclaimed film adaptation of Patricia Highsmith's The Price of Salt, Carol.

[60][61][62][63] The same year, Mara played Tiger Lily in the Joe Wright-directed fantasy film Pan, a role for which she received a great deal of criticism; she and Wright faced accusations of "whitewashing" a Native American character.

[66] She then starred alongside Ben Mendelsohn in Benedict Andrews' Una, which had its world premiere at the Telluride Film Festival on September 2, 2016.

[67] Mara next starred in Lion alongside Dev Patel and Nicole Kidman,[68] and The Secret Scripture, directed by Jim Sheridan.

[80] That same year, Mara starred opposite Phoenix again in Mary Magdalene, written by Helen Edmundson and directed by Garth Davis.

[81] This same year, she also collaborated with Joaquin Phoenix, Sia, Sadie Sink and Kat von D to narrate Chris Delforce's animal rights documentary Dominion.

[85] Following a brief hiatus, Mara co-starred in the neo-noir psychological thriller Nightmare Alley (2021), an adaptation of the 1946 novel of the same name directed by Guillermo del Toro.

In 2022, Mara starred with Frances McDormand, Claire Foy, Jessie Buckley and Ben Whishaw in Sarah Polley's feature adaptation of Miriam Toews’ bestselling novel Women Talking.