Born March 6, 1968 in Queens, New York, she is the third of six kids. Her father, Peter, was trained as a concert violinist. Her mother, Anne, is a nurse. Both are Irish immigrants. Moira was raised in Ronkonkoma, NY. She attended Connetquot Senior High School and graduated in the class of 1986. Later Moira attended Marymount Manhattan College. In 1984 Moira was cast in a small role in Connetquot Senior High School's production of Annie. Due to illness, the young woman playing Miss Hannigan was replaced, causing a series of cast changes. Director Eric Martinsen chose to recast Moira as Grace Farrell. She was a great success, and so began her career.
Listed as one of twelve "Promising New Actors of 1992" in John Willis' Screen World, Vol. 44. When cast in David Lynch's Twin Peaks: Fire Walk with Me, she came home to get permission from her priest to do her first sexual scene. She narrated the audio book for "jacob have I loved". She was initially contracted to play Polly Pry, the female lead in Trey Parker's Alferd Packer: The Musical but pulled out because she feared it would damage her serious movie career. Was originally cast as Kit Keller in A League of Their Own, but hurt her ankle on the set of The Cutting Edge. The role of Kit was given to Lori Petty. Her husband is a Texas businessman and she has two children by him. Her daughter is named Ella and was born in 2001, her son is named Eamon and was born in 2003. Was cast by director James Gray in Little Odessa because he was impressed by her performance in Twin Peaks: Fire Walk with Me. During the shooting of the film The Cutting Edge she spent over two months in figure skate training with her co-star D.B. Sweeney, they became close friends and remain so to this day.