Date of Birth: October 31st 1963
Mulroney was born in Alexandria, Virginia to Ellen, a housewife and amateur actress originally from Manchester, Iowa, and Michael Mulroney, a law professor 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. Mulroney's ancestors immigrated from Donegal and Mayo in Ireland during the Irish Potato Famine; he is of mostly Irish descent, although one of his grandmothers way back 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. 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 Phi Gamma Delta fraternity. His college girlfriend Aki Alessandra, who was a year older than Mulroney, got married to him just after graduation.
Mulroney co-starred in Young Guns and first gained notice in the film Longtime Companion, portraying an HIV victim during the early days of the outbreak of the virus, who becomes the first of his group of friends to succumb to the disease. 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 co-starred in The Wedding Date, as Debra Messing's escort to her sister's wedding. He was also in the ensemble film The Family Stone starring Sarah Jessica Parker. Mulroney played Gavin Mitchell on the TV series, Friends. His character dated Rachel for one episode but they broke up when it became too complicated between them because of Ross.
In 1993, he wrote the song 'Someone Else's Used Guitar' for Peter Bogdanovich's The Thing Called Love. Dermot also is credited as a song performer on the movie and for four other tunes, as well as acting in the movie.
Mulroney married actress Catherine Keener in 1990 after they met in 1987 when filming Survival Quest. The couple separated in May 2005 and filed for divorce June 11, 2007, citing irreconcilable differences. They have a son named Clyde, born June 1999. Mulroney, along with his brother Sean, owns Double Door, a Chicago music club. Dermot also plays in a band called the Cranky George Trio.