The seat had become vacant on when the constituency's Labour Member of Parliament (MP), Edward Williams, had been appointed as High Commissioner to Australia.
Labour selected John Evans, an official in the South Wales Miners' Federation who had stood unsuccessfully for the party in Montgomeryshire at the 1929 general election.
[1] Plaid Cymru reselected Trefor Richard Morgan, a former coal miner who was working in farming.
[1] The Manchester Guardian observed that Morgan was putting "a great deal of effort" into his campaign, and hoped to attract votes from supporters of the Conservatives, Liberals and Communists.
The paper speculated that, although he was likely to save his deposit, he would be likely to receive fewer than 4,000 votes, while Evans might take as many as 28,000.