Conservative deputy chairman Angela Browning has announced she will step down at the next general election.
Mrs Browning has been an MP since 1992
Mrs Browning, 59, has been a Tory MP since 1992, was an agriculture minister under John Major's government, and has held several shadow ministerial posts.
She said she was proud to have represented Tiverton and Honiton, but wanted to give her successor time to prepare for the next election.
The Devon seat is held by the Tories with a majority of more than 11,000.
Mrs Browning ran John Redwood's unsuccessful leadership campaign after Mr Major's resignation, then became an opposition education spokeswoman under William Hague.
She has also been shadow trade and industry secretary and shadow leader of the house.
She was made deputy chairman by David Cameron after he was elected leader last year.
She said: "I am immensely proud to have been elected to represent my home constituency where I have lived for nearly 40 years.
"I felt it right to make my announcement today in order that my successor can have sufficient time to prepare for the next election."