2025 Caerphilly by-election

The 2025 Caerphilly by-election was held on 23 October 2025 to elect the new member of the Senedd (MS) for the Senedd constituency of Caerphilly following the death of Hefin David on 12 August 2025. Former Senedd member Lindsay Whittle of Plaid Cymru won the by-election with 47% of the vote, ending more than a hundred years of Labour representation in UK Parliament and Senedd elections in Caerphilly, and outperforming expectations of a closer race between Plaid Cymru and Reform UK. Voter turnout was 50 %, the highest ever for a Senedd by-election. The election left the incumbent Labour government with a minority of 29 out of 60 seats. This was the fifth Senedd by-election to be held since its formation as the National Assembly for Wales in 1999 and the first since it changed its name to the Senedd in 2020. It was also expected to be the last Welsh Senedd by-election in its foreseeable future, as pending reforms to the Senedd's electoral system in 2026 were to introduce a closed list system of proportional representation, filling vacant constituency seats using the party list.