Gibson was born in Charleston, South Carolina, to Charles M. "Mac" and Beth Gibson. His mother was a social worker, and his father was a lawyer and liberal Democrat who served in the South Carolina state Senate and House. He is Roman Catholic. Gibson's interest in the performing arts began at a young age. Gibson was fascinated with Louis Armstrong. He and his sister were on a swim team together and they frequented a pizza parlor after their swim meets. It was at this pizza parlor that Gibson would sing along with a Dixieland band, complete with his attempt at a Louis Armstrong voice.