Aisling O'Sullivan (born 1968 in Tralee, County Kerry) is an Irish actress who starred in the movie The Butcher Boy as Francie's mentally unstable mother.
O'Sullivan attended the Gaiety School of Acting in Dublin and joined the Abbey Theatre in 1991.
At the National Theatre she has played in Liolà, Mutabilitie, and The Cripple of Inishmaan.
She played the role of Aileen Beck in the "Best Boys" episode of the 1995 TV series Cracker.
O'Sullivan appeared briefly in another Neil Jordan film, Michael Collins and had a part as the grieving mother who commits suicide in Six Shooter, playwright Martin McDonagh's Oscar-winning short film.
She is familiar to Irish television audiences as Dr. Cathy Costello from Series 1 to Series 5 in the drama series The Clinic, a role for which she has won an Irish Film and Television Awards best actress award in 2008.
She garnered major acclaim for her performance as Widow Quin in Druid Theatre Company's 2004 production of The Playboy of the Western World, which toured throughout Ireland including her native Kerry, and also starred Cillian Murphy and Anne-Marie Duff. In 2011 and 2012, she toured Ireland again with Druid, playing the titular character in Big Maggie by John B. Keane and was consequently nominated for Best Actress in the Irish Times Irish Theatre Awards. She also had a leading role in the Channel 4 thriller Shockers (1999). She is currently starring in Raw, an RTÉ drama based on a restaurant, playing restaurant manager Fiona Kelly, in its fifth season.