She was born into a musical family. Her father had been a fiddler, her mother a singer, and her brothers had their own group. She sang in her family's group in her youth, and her mother Patty had a song in her brothers' 1996 album, What A Time/Shay, by Michael and Martin Black.
Mary Black went on to play in other groups including the traditional Irish band, De Dannan from 1984–1986. Since 1986 she has had a successful solo career, where she went on to try contemporary styles ranging from jazz to country.
She is married to Joe O'Reilly of Dara Records and they have three children, Conor, Danny and Roisin.