Former Prime Minister David Cameron is standing down as an MP, triggering a by-election in his Witney seat.
Mr Cameron said he had “thought about this long and hard over the summer”, deciding it was “the right thing to do to stand down”.
He added: “In my view, in modern politics, with the circumstances of my resignation, it isn’t really possible to be a proper backbench MP.
Mr Cameron said he would continue to live in the constituency and support local causes, adding “but obviously I’m going to have to start to build a life outside Westminster”.
“I hope I’ll continue to contribute in terms of public service and of course contribute to this country I love so much.”
He said he had spoken to current Prime Minister Theresa May about his decision and she had been “very supportive”.
In March, he had said he intended to stand again for Witney, telling the BBC: “I love being MP for Witney and am very keen to continue”.
Mr Cameron, 49, was first elected as Witney’s MP in 2001, becoming Conservative leader after the 2005 General Election and entering No 10 as coalition Prime Minister in 2010.
He resigned as Prime Minister on 24 June this year, just hours after Britain voted to leave the European Union.