Peet was born in New York City, the daughter of Penny (nee Levy), a social worker, and Charles Peet, a corporate lawyer. During her four-year period of study with Hagen, Peet appeared in the off-Broadway revival of Clifford Odets's Awake and Sing. Her early roles included a guest role on the television series Law & Order. In 2005, Peet appeared in the play This Is How It Goes, filling in for Marisa Tomei at the last minute after six days of rehearsal. She will also play an FBI agent in 2008's Untitled X-Files Sequel. Peet married screenwriter David Benioff (whom she met on a blind date) on September 30, 2006 in New York City and gave birth to a daughter, Frances Pen, on February 20, 2007.