Davies was born in Canning Town, London to Welsh parents.
He became well known for playing the part of Battery Sergeant Major Williams in the 1970s British sitcom It Ain't Half Hot Mum. His catchphrase on the show was "Shut Up!" delivered with a ear drum shattering military scream. As a spin-off from the series, Davies and his co-star, Don Estelle had a number one hit in the UK with a semi-comic version of Whispering Grass.
He is also know for providing the voice of Sergeant Major Zero in the Terrahawks television series.