David Cameron is to stand down as MP for Witney, triggering a by-election in the Oxfordshire seat, he has announced.
Mr Cameron told ITV News that he had thought "long and hard" over his choice but had ultimately decided that he would be a "distraction" from the work of government.
George Osborne has said that David Cameron's resignation from parliament is a "sad day" in a tribute to his key political ally.
Osborne, who served as treasurer under Cameron, said he was sad to see his "great friend" leave British politics.
"I will miss him alongside me on the green benches over the coming years," he wrote on Twitter.
Cameron said he would stay on as Witney MP after resigning as PM - but he said in practice it was an impossible switch.
The former prime minister has stepped down from his position in parliament as he resigned his seat as the MP for Witney.
He rose to lead the country before an equally dramatic downfall after failing to persuade the public to vote to remain in the EU.