- Speaking outside Downing Street, she promised a "national renewal" under her successor.
- May will now travel to Buckingham Palace to formerly offer her resignation.
- Boris Johnson will arrive shortly afterwards and meet the Queen, at which point he will be appointed prime minister.
LONDON Theresa May has resigned as prime minister, using her valedictory speech to promise a "national renewal" under her successor.
May, who resigned after parliament rejected her Brexit plan three times, had lunch with her husband Philip on the terrace of Downing Street before making a speech on the steps outside.
"I am about to go to Buckingham Palace to tender my resignation to Her Majesty The Queen," May said.
"I repeat my warm congratulations to Boris on winning the Conservative leadership election. I wish him and the government he will lead every good fortune in the months and years ahead.
"Their successes will be our country's successes, and I hope that they will be many."
Shortly before, she led her final Prime Minister's Questions, where she appeared tearful, and where Conservative MPs offered her a standing ovation as she left the chamber.
She offered a lukewarm reception to incoming prime minister Boris Johnson, who resigned from Cabinet last year in protest at her Brexit plan, and signed off by urging Jeremy Corbyn to follow her lead and resign as party leader.
Responding to Corbyn's question, in which he asked if May agreed that Johnson had no mandate and should call a general election, the prime minister said she didn't.
"I am pleased to hand over to an incoming leader of the Conservative party and prime minister, who I worked with when he was in my cabinet, and who is committed as a Conservative who stood on a Conservative manifesto in 2017 to delivering on the vote of the British people in 2016 and to delivering a bright future for this country," she said.
Addressing Corbyn, she said: "Perhaps I could finish my exchanges with him by saying this: as a party leader who has accepted that her time was up, perhaps the time is now for him to do the same."
Watch Theresa May given standing ovation at final PMQs
May is now travelling to Buckingham Palace to offer her resignation. Boris Johnson will arrive shortly after and tell the Queen he is able to form a government, at which point he will be appointed prime minister.
Johnson, who yesterday beat Jeremy Hunt in the Conservative leadership contest, will spend the afternoon appointing members of his new Cabinet, and is expected to install vocal Brexiteers into many senior positions.
Sajid Javid is expected to be named Chancellor, while Dominic Raab has been tipped for Foreign Secretary.
Priti Patel, the former international development secretary, has reportedly been lined up as Home Secretary, while Michael Gove is being considered for the role of Duchy of Lancaster, which would effectively make him the deputy prime minister.
Cummings is disliked by many Conservative MPs, and in particular by those who belong to the European Research Group of hardline Brexiteers in the party, having sidelined many of its more vocal members during the EU referendum campaign.
Cummings, who has not served in government since the 2016 referendum, described members of the European Research Group many of whom backed Johnson's leadership campaign as a "narcissist-delusional subset," which attempted to destroy Vote Leave and should be "treated like a metastasising tumour and excised from the UK body politic."