The Senedd Cymru (Members and Elections) Act 2024 (sometimes referred to as the Senedd Reform Act) is an act of Senedd Cymru expanding and reforming the Senedd (Welsh Parliament; Welsh: Senedd Cymru) in Wales. Provisions of the act include creating sixteen larger constituencies, each electing six members of the Senedd (MSs) by proportional representation.

The bill was introduced to the Senedd on 18 September 2023, received royal assent on 24 June 2024, and the changes it makes to the Senedd's electoral system will be introduced in the 2026 Senedd election.

The Richard Commission report of 2004 suggested an increase in the number of Members to 80. That number was also suggested, as a minimum, by the 2014 report of the Silk Commission. Similarly, in 2013 and 2016, the Electoral Reform Society published reports making the case for enlarging the Assembly. A 2017 report of an expert commission led by Laura McAllister suggested an increase to between 80 and 90 Members, switching to single transferable vote (STV) and enforcing gender quotas. There was no cross-party consensus, however, on any of these measures in 2017.

As part of the 2021 co-operation agreement between Welsh Labour and Plaid Cymru, the parties agreed on an expansion of the Senedd to between 80 and 100 Members and a more proportional voting method, one that integrates gender quotas. Paragraph 22 also asked for recommendations to be made by the Special Purpose Committee by 31 May 2022, and aimed to pass legislation in the ensuing 12 to 18 months so that the it can be applied for the next election in 2026.

A Special Committee was set up on 6 October 2021, composed of five members representing each party, as well as the Llywydd of the Senedd. They held public and private meetings on the issues. In May 2022, a joint position statement was published by First Minister Mark Drakeford and Plaid Cymru Leader Adam Price, and sent to the Special Committee. In it, they called for a 96-Member Senedd, all elected through closed party list proportional representation (using the D'Hondt method) with mandatory "zipping" of male and female candidates in the list to ensure that for every party, half of the candidates will be women (unlike the voluntary all-women shortlists used by the Labour Party). With a reduction in the number of Welsh MPs and new constituency boundaries being proposed for the next UK general election, the Senedd elections were proposed to be organised in 16 six-member regions created by pairing up the 32 redrawn Westminster constituencies.

The final report of the Special Committee was published on 30 May 2022 and recommended the system agreed to by the Labour and Plaid Cymru leaders. Although the Expert Panel preferred the single transferable vote to any other method, the closed list PR system was favoured by the Committee over its capacity to enforce gender quotas through mandatory zipping, although the gender quotas rule was later abandoned. The report was discussed in plenary session on 8 June 2022, and approved 40–15.

In February 2023, plans for additional reform included:

In September 2023, it was also proposed job sharing among Welsh Government ministers also be considered.