 He slowly worked his way up in the theatre, becoming a call boy (telling actors when they were due on stage) at His Majesty's Theatre and later a prompter, stage manager, understudy, and then moving on from smaller parts with good reviews to larger, better parts.Rains moved to America in 1913 due to the opportunities that were being offered in the New York theatres.However, at the outbreak of World War I the following year, he returned to England to serve in the London Scottish Regiment, alongside fellow actors Basil Rathbone, Ronald Colman, Herbert Marshall and Cedric Hardwicke.