Dermot Mulroney (born October 31, 1963) is an American actor.
Mulroney was born in Alexandria, Virginia, the son of Ellen, a housewife and amateur actress originally from Manchester, Iowa, and Michael Mulroney, a law professor (and amateur racecar driver) at Villanova University School of Law, originally from Elkader, Iowa. He has a sister, Moira, and three brothers, Conor, Kieran (who is also an actor), and Sean. Moira formerly worked in the Philadelphia DA's office as an assistant district attorney and is currently employed by WXPN, an FM radio station in Philadelphia. Mulroney's ancestors immigrated from County Donegal and County Mayo in Ireland during the Irish Potato Famine; he is of mostly Irish descent, although one of his grandmothers was German American. Mulroney attended Maury Elementary School and played cello in school and city youth orchestras, as well as acting in children's community theater. Mulroney attended the Interlochen Arts Camp as a cellist. He later attended T. C. Williams High School (grad. 1981), the high school portrayed in Remember the Titans, as well as Northwestern University (grad. 1985) in Evanston, Illinois, where he was a member of the fraternity of Phi Gamma Delta.
Most of his lead performances have been in romantic comedy films. Mulroney has appeared in many movies, including as the male lead in My Best Friend's Wedding alongside Julia Roberts and Cameron Diaz. He is probably best known for his western roles as either an outlaw or gunman. Mulroney co-starred in the 1988 western Young Guns, for which he is possibly best known, in which he played "Dirty Steve" alongside Emilio Estevez, and in 1994 he starred alongside Mickey Rourke in The Last Outlaw, which has since become a cult classic among western genre fans. Mulroney also played the love interest of Madeleine Stowe in the western Bad Girls. He first gained critical acclaim in the film Longtime Companion, portraying a young man with HIV during the early days of the outbreak of the virus, who becomes the first of his group of friends to succumb to the disease. He was also in the ensemble film The Family Stone starring Sarah Jessica Parker. In 2005, he played a "date-for-hire" character alongside Debra Messing in The Wedding Date.