Dermot Mulroney grew up in Alexandria, Virginia, and went to Maury Elementary School. He played the cello in school and city youth orchestras and acted in children's community theater. He made his high school stage debut in an awful play called "Are Teachers Human?" at George Washington Middle School. He graduated from T.C. Williams High School in 1981. His dad was a lawyer. He grew up with three brothers - Sean, Conor and Kieran Mulroney (now also an actor) - and a sister named Moira.
Graduated from Northwestern University in 1985, where he attended the School of Speech. Was in a band called 'The Low & Sweet orchestra'. Was a member of Phi Gamma Delta fraternity at Northwestern University. Sister Moira works in the Philadelphia DA's office as an assistant district attorney. First child born, with Catherine Keener, a son named Clyde. [June 1999] Mulroney's younger brother Kieran Mulroney is also an actor. The brothers starred together in the John Hughes comedy, Career Opportunities with Jennifer Connelly and Frank Whaley. He and his older brother Sean are co-owners of 'The Double Door', one of Chicago's more popular music clubs. Mulroney has been married to actress Catherine Keener since 1990. They met in 1987 when filming Survival Quest. Plays cello in the song "Place Your Hand" from Melissa Etheridge's 1992 Album "Never Enough". Good friends with Brad Pitt. Born on the same day as actor/comedian Rob Schneider. Plays double bass and cello on the debut EP of Rain and Summer Phoenix's band, Papercranes. Lives in Los Angeles. He is sometimes confused with actor Dylan McDermott; there is a slight resemblance and a similar sounding name. Is of predominantly Irish ancestry. All of his siblings have traditional Irish names Plays in a band called the Cranky George Trio. Played the cello on the score to Mission: Impossible III. Attended "TC Williams High School", which later became the setting of a Disney movie with Denzel Washington. Brother-in-law of Elizabeth Keener.