A by-election was called following the death of Tom Hooson, the Conservative MP for Brecon and Radnorshire, in 1985. Tom Hooson had been the MP for the constituency since the Conservatives came to power in 1979.

There were seven parliamentary candidates standing in this by-election; Richard Livsey (Liberal Alliance), Richard Willey (Labour), C. J. Butler (Conservative), Mrs. Janet Davies (Plaid Cymru), David Sutch (Official Monster Raving Loony Party) and two Independent candidates.

The by-election was held at a very difficult time for the Conservative Government and this particular by-election was given wide coverage in the British press. The Conservatives were surprised when a seat they regarded as a safe one was lost to Richard Livsey, the Liberal Alliance candidate.

This was a time when the coalition between the SDP and the Liberal Party, under the name Alliance, was gaining increasing support. The Social Democratic Party was formed in 1981, mainly by former members of the Labour Party who were unhappy with Labour left wing policies and saw a chance for a third party to make its mark on British politics. Among the most well known leaders of the SDP within Wales were Tom Ellis and Gwynoro Jones.

Like the SDP, the Liberals took advantage of the voters' discontent with the two main parties in 1985 and the Alliance succeeded in defeating the Conservatives and Labour in the Brecon and Radnorshire by-election.