The by-election was held due to the incumbent Liberal MP, Samuel Thomas Evans becoming President of the Probate and Divorce Division of the High Court of Justice.
[1] The Mid Glamorgan Liberal and Labour Association selected Frederick Gibbins to fight the seat.
Gibbins was initially reluctant having given certain private assurances that he would not contest the election but he was prevailed upon to change his mind and having consulted his close friends (and perhaps getting the permission of his wife), he agreed to stand.
[2] The by-election was acrimonious because it signalled a rupture between the Liberals and organised Labour in the area, especially the South Wales Miners Federation.
It also caused internal conflicts within the South Wales Miners Federation, with William Brace, their Vice-President, opposing the intervention of a Labour candidate.