Long-serving Liberal Democrat MP and former minister Don Foster is to stand down from Parliament at the next election, scheduled for May 2015.
The 66-year-old former science teacher has served as MP for Bath since 1992 and was a minister in the Department for Communities and Local Government from 2012 until being made the Lib Dems' chief whip in the Commons in last October's reshuffle.
Mr Foster snatched the Bath seat from then Conservative chairman Chris - now Lord - Patten in one of the biggest upsets of the 1992 election. He successfully defended the seat in four elections, increasing his majority to 11,883 in 2010.
Announcing his intention to stand down, Mr Foster said: "After what will have been 23 wonderful years, this has been a very difficult decision to make. It has been an enormous privilege since 1992 to serve the people of this great city through five parliamentary sessions.
"However, my task is not over: there are 17 months before the next election. I have every intention of continuing to do all I can to work with and for local people. I will do my utmost to ensure that Bath continues to grow from strength to strength as a great place in which to live and work."
Lib Dem leader and Deputy Prime Minister Nick Clegg said: "Don has been an outstanding MP and will be hugely missed by his constituents and his colleagues in Parliament. His energy, humour and tenacity are unrivalled and I have seen first-hand Don's tireless efforts to serve Bath as an MP and Britain as a minister.
"After 33 years as a public servant - as a local councillor on Avon County Council and as MP for Bath - Don will be hugely missed. And with five stunning victories behind him, he leaves big shoes to fill."
The executive of Bath and North East Somerset Liberal Democrats is to meet on Thursday to start the process of choosing a replacement candidate for the 2015 poll. Although Mr Foster enjoyed a comfortable 11% majority over his Conservative rival in 2010, party strategists will be worried that the loss of the "incumbency factor" may make the seat vulnerable to Tories.