Brecon and Radnorshire is also entirely within the preserved county of Powys, and within the Mid and West Wales region.

The region consists 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.

Montgomeryshire is one of two constituencies covering Powys, both entirely within the preserved county, and both within the Mid and West Wales region.

The Mid and West Wales 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.