The 1939 Caerphilly by-election was a parliamentary by-election held on 4 July 1939 for the British House of Commons constituency of Caerphilly.
Morgan Jones was the previous member of Parliament. He died on 23 April 1939. He was a conscientious objector during the First World War.
Ness Edwards was a coal miner and during the first world war, a conscientious objector. Ronald Bell was a barrister, and later became a politician.