Education minister
Kirsty Williams has represented the Brecon and Radnorshire constituency for the Welsh Liberal Democrats since 1999, also serving as the party's leader in Wales for a total of eight years.
She told the Senedd it had been "a pleasure" to serve in the Welsh Parliament, where members had built, and were continuing to build, "a democracy fit for all the people of our nation".
Independent MS Lord Dafydd Elis-Thomas and Lib Dem MS Kirsty Williams hold positions in the current Welsh Government.
The minister said there was "honour in finding common ground for the common good across parties and policies".