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.
Theresa May has said she was "proud " to work in David Cameron's government as she thanked him for his service to the country.
The new prime minister said that the Conservatives had achieved "great things" under her predecessor as he resigned from parliament.
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.