After the completion of his graduation in 1992, Armstrong relocated to London with some of his friends to start his professional career in comedy and acting. While he was in search for acting roles, he got employed in a string of North London restaurants and bars and was later came in touch with Ben Miller.
Alexander Armstrong along with Miller collaborated together in four series of the famous show Armstrong and Miller. They did four seasons together from 1997 to 2001. They also performed sketches in The Sunday Format. The duo after tasting a considerable success decided to split in order to concentrate on their solo careers. Armstrong re-established his collaboration with Miller for the revamped version of the award-winning show The Armstrong and Miller Show in the year 2007.
Armstrong is a well-known TV presenter and garnered wide acclaim for his shows like ITV1 quiz series Don't Call Me Stupid, In addition to that he has served as a guest host on the BBC's mocking panel game Have I Got News for You.
After spending more than a decade in comedy and television, Armstrong came back to his musical roots and put forward all his skills in his cover band which is famous for playing a wide range of music from rock to jazz to classics to pop. He has been trained in classical music. In his band, he is the lead vocalist and is well supported by Simon Bates on woodwind, Harry the Piano on keyboards, Dave Swift on bass and Jeff Lardner on drums.