Brecon and Radnorshire (Welsh: Brycheiniog a Sir Faesyfed) was a county constituency in Wales of the House of Commons of the Parliament of the United Kingdom.

Radnorshire is included in full, and the only significantly populated area from Brecknockshire not in this constituency is Brynmawr, which is in Blaenau Gwent.

[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.

In the event, the swing to the Conservatives was 0.3%, and the Liberal Democrats retained the seat, with Roger Williams remaining the MP.

The political parties had been making preparations for an election to take place from 1939 and by the end of this year, the following candidates had been selected; The Labour candidate, Chris Mann, won the selection over future AMs Carwyn Jones and Jeffrey Cuthbert, and future AM and MP Peter Law.