The seat had become vacant on 10 February 1984. The constituency's Labour Member of Parliament (MP), Ioan Lyonel Evans (10 July 1927 – 10 February 1984), had died at the age of 56.
She had been a Member of the European Parliament (MEP) for Mid and West Wales 1979–1984 and had contested the Westminster seat of Denbigh in 1970. After winning the by-election, she held the seat until her retirement in 2019.
3. Clayton Francis Jones was nominated by Plaid Cymru. He was a 31-year-old coach operator and was a member of Taff-Ely Borough Council and Mid-Glamorgan County Council.
4. James Norwich Arbuthnot, a barrister born in 1952, represented the Conservative Party. He had been a Councillor in the Royal Borough of Kensington and Chelsea since 1978. Arbuthnot contested this constituency in 1983. He became a Conservative MP in 1987 and sat until 2015, when he joined The House of Lords.
5. Mrs Mary Winter represented the Communist Party. She was a senior social services officer with Mid-Glamorgan County Council and was aged 36 at the time of the by-election.
6. Noel Edmundbury Rencontre was an Independent candidate, who sought election under the ballot paper label Womble Independent.
7. Paul Nicholls-Jones was an Independent candidate.