List of by-elections to the Senedd

This is a list of by-elections to the Senedd (Welsh Parliament; Senedd Cymru; formerly known as the National Assembly for Wales).
 * Where seats changed political party at the by-election, the result is highlighted.

''*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.''