He is best remembered for playing Battery Sergeant Major Williams in the sitcom It Ain't Half Hot Mum (1974–1981) over its entire run.

The show's popularity resulted in Davies and his co-star Don Estelle achieving a UK number-one hit with a version of "Whispering Grass" in 1975.

[13] In September–October 1985, Davies played the lead role of George Vance, a museum custodian elevated to the peerage, in the six-part BBC Two comedy series The New Statesman.

)[16] Davies also featured in the BBC comedy sitcom Oh, Doctor Beeching!, written by David Croft and Richard Spendlove, as the Lord Mayor in an episode broadcast in 1997.

He played Mog in the Welsh rugby film Grand Slam (1978), and was a sergeant in the Highland Regiment in Adolf Hitler: My Part in His Downfall (1973) with Jim Dale and Spike Milligan.

[18] In 1989, he revived the role of Sergeant Major Williams in a 30-minute Royal Air Force training film, Hazardous Ops.

Davies' distinctive voice was heard in commercials for New Zealand's Pink Batts house insulations and confectionery ads for Cadbury's Wispa[20] and for Heinz Curried (Baked) Beans.

[23] In the 1970s, he read an edition of BBC Radio 4's Morning Story programme,[3] and also narrated the audiobook for the Ladybird children's classic Treasure Island.