Whilst at Cambridge, Armitage's interest in musical comedy grew, and he began writing popular songs, using the stage name Noel Gay in order to avoid embarrassing the church authorities. After contributing to reviews he was commissioned to write the score for the Charlot Show of 1926. His next show was Clowns In Clover, which starred Cicely Courtneidge and Jack Hulbert.
Gay's career quickly blossomed, due to his talent for writing catchy, popular melodies in styles ranging from music hall to operetta. He is the only composer besides Andrew Lloyd Webber to have had four shows running at the same time in London's West End.
His most famous show, Me and My Girl was originally performed at the Victoria PalaceLondon, in 1937, starring Lupino Lane. Me And My Girl ran for a phenomenal 1,646 performances. It was revived again in 1952, and 1984, when it ran for eight years initially at the Haymarket theatre, Leicester and then at the Adelphi theatre in London, later going on tour throughout Britain, and transferring to Broadway. The show's showstopper, "The Lambeth Walk" has the distinction of being the only popular song to be the subject of a leader in The Times. In October 1938 one of its leaders read 'While dictators rage and statesmen talk, all Europe dances - to The Lambeth Walk.'
Noel Gay Artists, now one of the leading British showbusiness agencies was formed by his son, Richard Armitage (born 1928) as a talent agency to supply singers to perform in Noel Gay hits.