Butler was born in Glasgow, Scotland, the son of Margaret and Edward Butler. For the first two years of his life, he lived in Montreal, Quebec. When his parents divorced, his mother took him and his siblings back to Scotland, to her hometown of Paisley. He had no further contact with his father until he was sixteen years old. Butler's father died of cancer when Gerard was 22.
Butler graduated from Glasgow University Law School before embarking on his early career in stage plays. His first roles were in Coriolanus and in the stage version of Trainspotting. Butler landed his Read his whole biography