It had been held since its formation in 1999 by the Plaid Cymru politician, Rhodri Glyn Thomas until his retirement in 2016.

It is now held by Plaid Cymru politician Adam Price, who became leader of the party in 2018.

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 constituency includes the whole of 41 Carmarthenshire communities (Abergwili; Ammanford; Betws; Cenarth; Cilycwm; Cwmamman; Cynwyl Gaeo; Dyffryn Cennen; Gorslas; Llanarthney; Llanddarog; Llanddeusant; Llandeilo; Llandovery; Llandybie; Llandyfaelog; Llanegwad; Llanfair-ar-y-bryn; Llanfihangel Aberbythych; Llanfihangel-ar-Arth; Llanfihangel Rhos-y-Corn; Llanfynydd; Llangadog; Llangathen; Llangeler; Llangunnor; Llangyndeyrn; Llanllawddog; Llanllwni; Llansadwrn; Llansawel; Llanwrda; Llanybydder; Llanycrwys; Manordeilo and Salem; Myddfai; Newcastle Emlyn; Pencarreg; Quarter Bach; St Ishmael; Talley).

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