Cynthia Ellen Nixon (born April 9, 1966) is an American actress, activist, and theater director. For her portrayal of Miranda Hobbes in the HBO series Sex and the City (1998–2004), she won the 2004 Primetime Emmy Award for Outstanding Supporting Actress in a Comedy Series. She reprised the role in the films Sex and the City (2008) and Sex and the City 2 (2010), as well as the television show And Just Like That... (2021–present). Her other film credits include Amadeus (1984), James White (2015), and playing Emily Dickinson in A Quiet Passion (2016).

Nixon made her Broadway debut in the 1980 revival of The Philadelphia Story. Her other Broadway credits include The Real Thing (1983), Hurlyburly (1983), Indiscretions (1995), The Women (2001), and Wit (2012). She won the 2006 Tony Award for Best Actress in a Play for Rabbit Hole, the 2008 Primetime Emmy Award for Outstanding Guest Actress in a Drama Series for Law & Order: Special Victims Unit, the 2009 Grammy Award for Best Spoken Word Album for An Inconvenient Truth, and the 2017 Tony Award for Best Featured Actress in a Play for The Little Foxes. Her other television roles include playing political figures Eleanor Roosevelt , Kade Prenall in NBC Hannibal Warm Springs (2005), Michele Davis in Too Big to Fail (2011), and playing Nancy Reagan in the 2016 television film Killing Reagan. In 2020 she appeared in the Netflix drama Ratched.

On March 19, 2018, Nixon announced her campaign for Governor of New York as a challenger to Democratic incumbent Andrew Cuomo. Her platform focused on income inequality, renewable energy, establishing universal health care, stopping mass incarceration in the United States, and protecting undocumented children from deportation. She lost in the Democratic primary to Cuomo on September 13, 2018, with 34% of the vote to his 66%. Nixon was nominated as the gubernatorial candidate for the Working Families Party; the party threw its support to Cuomo after Nixon lost in the Democratic primary.

Nixon has been an advocate for LGBT rights in the United States, particularly the right of same-sex marriage. She met her wife at a 2002 gay rights rally, and announced her engagement at a rally for New York same-sex marriage in 2009. She received the Yale University Artist for Equality award in 2013 and a Visibility Award from the Human Rights Campaign in 2018.