Kate Rooney Mara (/ˈmɛərə/ MAIR-ə; born February 27, 1983) is an American actress. She is known for her work in television, playing reporter Zoe Barnes in the Netflix political drama House of Cards (2013–2014; 2016), computer analyst Shari Rothenberg in the Fox thriller series 24 (2006), wronged mistress Hayden McClaine in the FX miniseries American Horror Story: Murder House (2011), Patty Bowes in the first season of the FX drama series Pose (2018), and a teacher involved with an underage student in the FX miniseries A Teacher (2020).

Mara made her film debut in Random Hearts (1999). She has since appeared in Brokeback Mountain (2005), We Are Marshall (2006), Shooter (2007), Transsiberian (2008), Stone of Destiny (2008), The Open Road (2009), Transcendence (2014), The Martian (2015), Fantastic Four (2015), Morgan (2016), Megan Leavey (2017), My Days of Mercy (2017), Chappaquiddick (2018), and Friendship (2024).

Kate Mara was born on February 27, 1983, in Bedford, New York. Her parents are Timothy Christopher Mara, an NFL scout and vice president of the New York Giants for player evaluation, and Kathleen McNulty Mara (née Rooney). She is the second of four siblings, with one older brother, Daniel; one younger sister, the actress Patricia "Rooney"; and one younger brother, Conor. Her ancestry is Irish, one quarter Italian, and smaller amounts of German, French-Canadian, and English. Her father is one of 11 children, through whom she has 20 aunts and uncles, and 40 cousins.

She is a great-granddaughter of both New York Giants founder Tim Mara and Pittsburgh Steelers founder Art Rooney Sr. Her mother's side of the family has held ownership in the NFL's Pittsburgh Steelers football team since its formation in 1933, and her father's side of the family has held ownership in the NFL's New York Giants since its formation in 1925. Her paternal grandparents were Wellington Mara and Ann Mara. Wellington co-owned the Giants football team from 1959 until his death in 2005, and was succeeded by his son (Kate Mara's uncle), John Mara, who is currently President, CEO, and co-owner of the team. Kate Mara's maternal grandfather, Timothy James "Tim" Rooney, has operated Yonkers Raceway in Yonkers, New York, since 1972. Her granduncle, Dan Rooney, chairman of the Steelers, was a former United States ambassador to Ireland and the co-founder of the charitable organization The Ireland Funds. Her first cousin, once removed, Art Rooney II, is the current president and co-owner of the Steelers.

Mara began acting at the age of nine in a school musical. She attended several youth theater-arts schools and appeared in community theater and in school plays. In an Esquire magazine interview, she says she was "painfully shy" growing up, adding she only had one friend.

Mara's first recurring television role was in the FX Drama Nip Tuck in a love triangle with her boyfriend Matt McNamara (John Hensley) and another cheerleader (Sophia Bush). Mara also appeared on Cold Case, Boston Public, CSI: Miami and CSI: Crime Scene Investigation.

Mara was cast as the lead in the 2004 The WB pilot Prodigy, about a teenage child prodigy. She had a recurring role on the WB's Jack & Bobby in 2005 and a five-episode arc on the Fox TV series 24 in 2006, playing computer analyst Shari Rothenberg. Mara joined the cast of the HBO comedy-drama Entourage for the series' sixth season in 2009. She played Brittany, Eric "E" Murphy (Kevin Connolly)'s assistant at his talent-management company and a potential love interest. Mara filmed four episodes for the series in 2009. In 2011, she guest starred on the FX horror series American Horror Story, as Hayden McClaine, a student who becomes Dr. Ben Harmon (Dylan McDermott)'s dead mistress, a spirit trapped in the Harmon house. Mara was offered the role by Ryan Murphy, her former producer on Nip/Tuck.

In 2012, Mara joined the cast of House of Cards, playing the part of Zoe Barnes, an intrepid reporter from Washington, D.C. who becomes a major ally to Frank Underwood by leaking stories that undermine his rivals. She filmed a second season of the series, which was released on February 14, 2014. On July 10, 2014, she was nominated for the Primetime Emmy Award for Outstanding Guest Actress in a Drama Series. She played a teacher who begins an illicit relationship with an underage student in the FX miniseries A Teacher (2020). For it, she received an Independent Spirit Award nomination for Best New Scripted Series as an executive producer.