It was triggered by the resignation of the incumbent Huw Irranca-Davies following his decision to contest the coterminous Ogmore constituency in the 2016 Welsh Assembly election.

The seat fell vacant after the incumbent MP, Huw Irranca-Davies of the Labour Party, chose to resign following his selection to contest the coterminous Ogmore constituency in the Welsh Assembly election.

[2][3] On 23 March 2016, Irranca-Davies was appointed Crown Steward and Bailiff of the Manor of Northstead the process by which resignations from the House of Commons are permitted.

Irranca-Davies had originally announced that he would seek Labour's nomination for the Welsh Assembly's Ogmore in October 2015, stating that if he was selected he would resign his Westminster seat.

Given that in both the Assembly and Westminster Ogmore was considered a safe seat for Labour his early resignation allowed the by-election to be held on the same day rather than forcing voters to go to the polls again a few weeks later.