An actor whose versatility is matched by the unpredictability of many of his career choices, Dermot Mulroney has been appearing in films since the early 1990s. Born in Alexandria, Virginia, on October 31, 1963, Mulroney developed an early interest in acting. After graduating from Northwestern University in 1985, he began acting in a number of made-for-TV movies, playing young men caught up in problematic teen romances in both Sin of Innocence (1986) and Daddy (1987). In 1988 he made his film debut in the Brat Pack western Young Guns, portraying one of the titular group of Old West gunslingers.
Despite the success of Young Guns, Mulroney remained a relative unknown, appearing in a number of forgettable films. One exception was Longtime Companion (1990), a seminal AIDS drama that cast him as a young man who becomes one of the virus' earliest casualties. The actor continued to pop up in films of widely varying subject matter, to say nothing of quality, starring in everything from teen comedies (Career Opportunities, 1991) to westerns (Bad Girls, 1994) to thrillers (Copy Cat, 1995) to chick flicks (How to Make an American Quilt, 1995). He also enjoyed a collaboration with director Tom Di Cillo, starring (and in the first case, associate producing) Di Cillo's Living in Oblivion (1995) and Box of Moonlight (1996). In 1997, Mulroney had one of his most high-profile roles to date as Julia Roberts' titular best friend in My Best Friend's Wedding, a successful black comedy that also starred Cameron Diaz and Rupert Everett.
Mulroney would spend the next several years enjoying a successful big screen career, with appearances in films like The Wedding Date, Zodiac, Burn After Reading, Big Miracle, and more.
Mulroney has also benefited from his collaborations with Di Cillo for more personal reasons: for some years he has been married to Catherine Keener, an actress often cited as the director's muse.