On television, he is best known for his roles as King Louis XIII in the BBC series The Musketeers and Ted Bundy in the TV film Serial Thriller: Angel of Decay. In the cinema, he played the Master of Laketown's deputy Alfrid Lickspittle in The Hobbit: The Desolation of Smaug and The Hobbit: The Battle of the Five Armies, and Ted Bundy again (identified as Him in the cast list) in the film Angel of Decay, which earned him a Best Actor Award at the British Independent Film Festival in 2016. In video games, Gage has portrayed Charibert in the Final Fantasy XIV expansion pack Final Fantasy XIV: Heavensward. In theatre, he has worked for the Royal Shakespeare Company on plays such as Hamlet, A Midsummer Night's Dream, and Macbeth.