Born in Manhattan Beach, California, Gibney moved to New York at a young age. She attended Buffalo State College for two years and eventually earned a Master of Fine Arts degree from the Yale School of Drama. Living in New York after school, she appeared in several off-Broadway productions. After working in Los Angeles for three years, Gibney returned to New York to refresh her theatre roots. She landed a permanent place in Hollywood in 1996.
Sixth of eight siblings. Worked as a New York chauffeur for 18 months to help pay for college. Has one daughter. Knows a few phrases in Swahili, Gaelic and Bulgarian. Is three-quarters Irish.