Sean McClory was born in Dublin, Ireland, but spent his early life in Galway. He was the son of Hugh Patrick, an architect and civil engineer, and Mary Margaret Ball, who had been a model.

Sean decided to become an actor and joined Dublin's renowned Abbey Theater (also known as the National Theater of Ireland, opened in 1904). He rose through the ranks playing in productions of the works of such authors as William Butler Yeats and George Bernard Shaw, and soon began to play leads mostly in comedies (popular through most of the 1940s and into the 1950s).