Butler was born in Paisley (Renfrewshire, Scotland), the youngest of three brothers and the son of Margaret and Edward Butler. His early years were spent in Montreal (Canada) and later returned to his home town after the separation of their parents. He grew up with his mother, who remarried a few years later. Had no contact with his father until sixteen. He studied law at the University of Glasgow, where he was president of the Society of Law School and worked as a lawyer after graduation.