The veteran Conservative Sir Michael Fallon is to stand down as MP for Sevenoaks after three decades.
Sir Michael said he planned to quit at the next election which could be just weeks away.
In a statement, he said: "Sadly I have decided that this parliament will be my last. I have served as an MP, for both Darlington and Sevenoaks, for more than 30 years – quite long enough.
"I want to thank all my constituents for their support and encouragement. Wendy and I will continue to live in the constituency and to be involved locally.”
The 67-year-old has one of the safest seats in the country and in the last election had a majority of more than 21,000.
He had reservations about Theresa May’s Brexit deal and had campaigned to remain in the EU at the referendum in 2016.
He was elected MP for Sevenoaks in 1997 having previously been MP for Darlington.
He has held a number of senior positions within the Conservative Party over the years, including a spell as Secretary of State for Defence.
Earlier this year it was rumoured that David Cameron was eyeing up the seat as he wanted to return to frontline politics.