Graduated from Northwestern University in 1985, where he attended the School of Speech.
Formerly in bands "The Low & Sweet Orchestra" and "Cranky George".
Was a member of Phi Gamma Delta fraternity at Northwestern University.
Has a son named Clyde Mulroney (born 1999) with first wife.
Mulroney's younger brother Kieran Mulroney is also an actor. The brothers starred together in the John Hughes comedy, Career Opportunities (1991) with Jennifer Connelly and Frank Whaley.
He and his oldest brother, Sean Mulroney, are owners of "The Double Door", one of Chicago's more popular music clubs.
Plays cello in the song Place Your Mind from Melissa Etheridge's 1992 album Never Enough, and in the score to Mission: Impossible III (2006).
Plays double bass and cello on the debut EP of Rain Phoenix and Summer Phoenix's band, 'Papercranes'.
Lives in Los Angeles.
All of his siblings have traditional Irish names (Conor, Kieran, Moira and Sean). Seven of his eight great-grandparents were of Irish descent, and one of his paternal great-grandmothers, Minnie Henrietta Musfeldt, was of German descent.
Attended T.C. Williams High School, which later became the setting of a Disney movie with Denzel Washington.
Both of his parents were originally from Iowa.
He got the scar on his lip from falling on a piece of glass when he was three.
Has 2 daughters, Mabel Ray Mulroney (born 2008) and Sally June Mulroney (born 2009) with wife, Tharita.
Mulroney appeared with James Garner in the 1988 theatrical film "Sunset". Years later, Mulroney inherited Garner's famous role of private detective Jim Rockford in the 2010 TV film "The Rockford Files".
Son-in-law of Emy Cesaroni and Franco Catullé.
Brother-in-law of Michele Mulroney. Former brother-in-law of Elizabeth Keener.
The April 5, 1989, issue of Variety, in the Film Production column, announced the movie "Nobody's Children" began filming March 13, 1989, in Madrid, Spain. Malcolm Clarke directed from a script by Peter Bart, who was also the producer. The cast included Dermot Mulroney. The film plot involved a gang of gypsy thieves. No evidence the film was ever completed or released.