Overview
- Plaid Cymru’s Lindsay Whittle won with 15,961 votes and 47.4% share, defeating Reform UK’s Llŷr Powell on 12,113 (35.9%) as Labour’s Richard Tunnicliffe finished on 3,713 (11.0%), a 3,848-vote majority.
- Turnout reached 50.43%, the highest for a Senedd election in Caerphilly since devolution began.
- Labour’s support collapsed by roughly 35 points from 2021, delivering a near 27-point swing to Plaid in a seat Labour had never previously lost.
- Reports from candidates and local parties point to tactical voting by smaller-party and left-leaning voters coalescing behind Plaid to keep Reform from taking the seat.
- The result immediately narrows the Welsh Government’s numbers for the next budget vote and reframes the contest ahead of the May 2026 election under a new proportional system that ends by-elections.