Colleen Rennison is of Irish, Scottish and French descent. She was born to Pat, a mortgage underwriter, and Cecilia Rennison, a television researcher, and was raised in Vancouver, British Columbia. She began her acting career with a role in the Canadian indie film Max in 1994. This was closely followed by appearances in a handful of television movies and a guest-starring role on the television series The Outer Limits. Carpool, starring Tom Arnold, David Paymer and Rachael Leigh Cook, was her first major American feature. Shortly after she landed a role in the John Dahl-directed Unforgettable with Ray Liotta and Linda Fiorentino, followed by Stargate SG-1 episode 'Bane' in 1998 with Richard Dean Anderson and Christopher Judge, followed by The Story of Us (1999), directed by Rob Reiner and featuring Bruce Willis and Michelle Pfeiffer, in which she portrays their daughter Erin. Her next major role was playing Mona Hibbard as a young girl (Minnie Driver played the character as an adult) in the film Beautiful, directed by Sally Field, also starring Joey Lauren Adams and Kathleen Turner.