Moira Kelly was born the third of six children in Queens, New York City, in March of 1968; her father was a professional violinist and her mother, a nurse. Inspired by classical and big band music, young Kelly followed in her father's musical footsteps by trying her hand at the violin, drums, and flute. Kelly was raised in Ronkonkoma, NY, and competed in opera while attending Connetquot High School in the mid-'80s. It was there that the acting bug bit, and when Kelly was cast in a small role in the high school's production of Annie, her role was unexpectedly expanded as the actress playing Miss Hannigan fell ill and Kelly was recast as Grace Ferrell. Rounding out her education at New York City's Marymount Manhattan College, Kelly worked a series of odd jobs while attending college in order to finance her education. Facing an important life decision, Kelly began to weigh her childhood dream of becoming a nun against a busy life in the limelight. Convinced by her priest that acting may be part of God's larger plan for her, Kelly eagerly began work on her first feature.

Kicking off her career with a made-for-television feature entitled Love, Lies & Murder, Kelly would soon transition to the big screen, appearing in Billy Bathgate and the popular ice skating movie The Cutting Edge. Subsequently replacing Lara Flynn Boyle in director David Lynch's Twin Peaks: Fire Walk With Me, the conflicted Kelly once again approached her priest to ask for guidance in a film that contained frank and explicit sexuality. Next drawing attention in dual roles as cinema legend Charles Chaplin's first love and fourth wife in Richard Attenborough's Chaplin, it was obvious to many that Kelly had a bright future ahead of her. Kelly's diversity truly began to shine in the mid- to late '90s, and though such films as Little Odessa (1994) and Changing Habits (1997) may not have found wide release or reached blockbuster status, the people who did happen to catch them when they were released on video found her performances as moving as ever. Rounding out the decade with everything from vocal work in The Lion King (1994) to a role as social activist Dorothy Day in Entertaining Angels: The Dorothy Day Story. She would next tackle the small screen with a role on The West Wing, and spent the next several years appearing on TV with the show One Tree Hill, as well as with other film projects like The Safety of Objects and Two Tickets to Paradise.