Gibson was born on January 3, 1956 in Peekskill, New York, the sixth of eleven children, and the second son of Hutton Gibson and Irish-born Anne Patricia (née Reilly, died 1990). His paternal grandmother was opera contralto Eva Mylott (1875–1920), who was born in Australia to Irish parents.

One of Gibson's younger brothers, Donal, is also an actor. Gibson's first name comes from Saint Mel, fifth-century Irish saint, and founder of Gibson's mother's native diocese, Ardagh, while his second name, Colm-Cille, is also shared by an Irish saint and is the name of the parish in County Longford where Gibson's mother was born and raised.

Mel Gibson's Family Tree