List of by-elections to the Senedd

This is a list of by-elections to the Senedd (Welsh Parliament; Welsh : Senedd Cymru; formerly known as the National Assembly for Wales).

Where seats changed political party at the by-election, the result is highlighted.

Assembly term	By-election	Date	Incumbent	Party		Winner	Party		Cause	Retained at next election
2021–2026	Caerphilly	23 October 2025	Hefin David		Labour	TBC		TBC	Death [1]	N/A
2016–2021	Alyn and Deeside	6 February 2018	Carl Sargeant		Labour	Jack Sargeant		Labour	Death (suicide) [2]	Yes
2011–2016	Ynys Môn	1 August 2013	Ieuan Wyn Jones		Plaid Cymru	Rhun ap Iorwerth		Plaid Cymru	Resignation to lead the Menai Science Park	Yes
2003–2007	Blaenau Gwent	29 June 2006	Peter Law *		Labour	Trish Law		Independent	Death (brain tumour)	Yes
1999–2003	Swansea East	27 September 2001	Val Feld		Labour	Valerie Lloyd		Labour	Death (cancer)	Yes

*Peter Law left the Labour Party and sat as an independent prior to his death. The by-election was won by his widow, but is classed as an independent gain from Labour.

See also

• List of by-elections to the Scottish Parliament
• Regional member changes to the Senedd

References

1. "Welsh Labour politician Hefin David dies, aged 47". BBC News. 13 August 2025. Retrieved 13 August 2025.
2. "Sacked Labour minister Carl Sargeant found dead". BBC News. 7 November 2017. Retrieved 12 July 2021.