It is also one of eight constituencies in the Mid and West Wales electoral region, which elects four additional members, in addition to eight constituency members, to produce a degree of proportional representation for the region as a whole.

It has been represented since its creation in 1999 by Plaid Cymru's Elin Jones, who has also been the Llywydd (Presiding Officer) of the Senedd since 2016.

The region consisted of the eight constituencies of Brecon and Radnorshire, Carmarthen East and Dinefwr, Carmarthen West and South Pembrokeshire, Ceredigion, Llanelli, Meirionnydd Nant Conwy, Montgomeryshire and Preseli Pembrokeshire.

The region consists of the constituencies of Brecon and Radnorshire, Carmarthen East and Dinefwr, Carmarthen West and South Pembrokeshire, Ceredigion, Dwyfor Meirionnydd, Llanelli, Montgomeryshire and Preseli Pembrokeshire.

For Westminster purposes, the same new constituency boundaries became effective for the 2010 United Kingdom general election.