William Mellows was born in Ashton-under-Lyne, Manchester, where his father, Staff Sergeant William Mellows, was then stationed. His father had ambitions for the son to become the fourth generation of the family to serve in the armed forces, but after they moved back to Ireland, Liam became steadily disillusioned with the British Government. He lived in Dublin for a time and spent a lot of time living in his grandparents house in Co Wexford, where his mother came from.