During the First World War he served with the Essex Regiment. He received injuries that left his face partially scarred and paralysed. In his acting career he would use this injury to good effect, by showing the unblemished side of his face when playing comedy or romance and the scarred, paralysed side of his face when playing drama or tragedy. After the war, Banks joined the Birmingham Repertory Theatre. He returned to London in 1921, and established himself as a leading dramatic actor and West End star known for his powerful yet restrained performances.