Brecon and Radnorshire (Welsh: Brycheiniog a Sir Faesyfed) is a county constituency in Wales of the House of Commons of the Parliament of the United Kingdom. Created in 1918, it elects one Member of Parliament (MP) by the first-past-the-post system of election. The constituency is represented by Fay Jones of the Conservative Party, who defeated incumbent Jane Dodds of the Liberal Democrats at the 2019 general election.

The constituency is set to be abolished, as part of the 2023 Periodic Review of Westminster constituencies and under the June 2023 final recommendations of the Boundary Commission for Wales for the next United Kingdom general election. The entire constituency would be part of Brecon, Radnor and Cwm Tawe.^[3]

The boundaries of the constituency correspond broadly with the ancient counties of Brecknockshire and Radnorshire. Radnorshire is included in full, and the only significantly populated area from Brecknockshire not in this constituency is Brynmawr, which is in Blaenau Gwent. This is the largest constituency in England and Wales by area.^[4] No town in the constituency exceeds a population of 10,000, the largest being Ystradgynlais at roughly 9,000. Other towns in the constituency are Brecon, Knighton, Crickhowell and Llandrindod Wells. The remainder of the constituency is largely made up of small villages and land used for farming sheep: sheep outnumber humans in Powys as a whole by around ten to one.^[5]

Under planned constituency changes announced in September 2016 ahead of the next general election, it was proposed to merge this seat with the southern half of Montgomeryshire, including Newtown, to form a new constituency called Brecon, Radnor and Montgomery.^[6]

The constituency was created in the boundary changes of 1918 by merging Breconshire and Radnorshire, both previously constituencies in their own right. As part of the Third Periodic Review of Westminster constituencies there were changes to the boundaries in 1983, when the constituency lost several small areas in the south.^[7] While once a Labour stronghold, the constituency was captured from the Conservative government by the SDP–Liberal Alliance at a dramatic by-election in 1985. It was regained by the Conservatives in 1992, taken back by the Liberal Democrats in 1997, and then returned to the Conservatives in 2015. It was the Conservatives' fifteenth target seat at the 2005 election, but the party's share of the vote fell, leaving it as the Conservatives' 95th target seat in 2010, requiring a swing of 5.09%. In the event, the swing to the Conservatives was 0.3%, and the Liberal Democrats retained the seat, with Roger Williams remaining the MP. In 2015 the seat was reclaimed for the Conservatives by Chris Davies, whose majority of 5,102 was the largest in the constituency since Tom Hooson won the seat, also for the Conservatives, in 1983. Roger Williams stood for the Liberal Democrats in 2015 but shed over 6,500 votes from his 2010 result, a loss of 17.8%.

In 2019, Davies pleaded guilty to filing false expenses claims, triggering a recall petition, the third such petition in the UK. The petition was successful, forcing Davies to vacate the seat.^[8][9] A by-election was held on 1 August, which was won by Liberal Democrat candidate Jane Dodds.^[10] Dodds was then defeated by Conservative Fay Jones at the general election in December 2019.

• Brecon and Radnorshire (Senedd constituency)
• List of parliamentary constituencies in Powys
• List of parliamentary constituencies in Wales