Boris Johnson has won the race to become the Conservative leader - and the next Prime Minister - defeating rival candidate Jeremy Hunt by 45,497 votes.
The final result of the ballot was:
Boris Johnson – 92,153Jeremy Hunt – 46,656
Mr Johnson will officially enter 10 Downing Street tomorrow (Wednesday) after winning over a majority of Tory members.
Boris Johnson poll
The controversial former Mayor of London's win could spark more Government resignations after Sir Alan Duncan quit as Foreign Office minister on Monday in protest at his expected victory, predicting a "crisis of government" if Mr Johnson becomes PM.
Ministers opposed to his "do or die" pledge to pull the UK out of the EU on October 31, even if there is no deal in place, could leave before Mrs May formally gives up the premiership on Wednesday afternoon.
Jeremy Hunt the Foreign Secretary and Johnson's rival (Getty)
A challenging start
Chancellor Philip Hammond and Justice Secretary David Gauke have given notice that they will resign rather than serve under Mr Johnson.
Mrs May will tender her resignation to the Queen after taking Prime Minister's Questions in the Commons on Wednesday afternoon for the final time, with the new Tory leader set to enter Number 10 soon afterwards.
The new prime minister will have to govern with a Tory-DUP majority of just two, after Dover MP Charlie Elphicke had the Conservative whip suspended when he was charged with sexually assaulting two women.
The Government majority could be further reduced next week if the Tories lose the Brecon and Radnorshire by-election.
Can an anointed PM be successful?
Previous Prime Ministers who have been anointed by their party rather than winning at a General Election have included Sir Winston Churchill, Harold Macmillan, Sir John Major, Gordon Brown and Theresa May.
Speaking to PA, politics professor John Curtice from Strathclyde University said: "Very often a prime minister who inherits the job in midterm is inheriting the fag end of a term.
"That was certainly true of Callaghan whose government then hit all sorts of trouble. I think Douglas-Home - that is one of the reasons Macmillan went because the polls were way behind.
"One of the reasons Theresa May has gone is because of the position of the Conservative Party in the opinion polls, which Boris is going to have to turn around.
"Major succeeded, he did very well in 1992 - so I guess what I am arguing is that you cannot suggest that becoming prime minister by being elected necessarily imbues you with some magical powers.
"Sure, yes, those are probably the more favourable circumstances to which to come to office, because then you do so replacing the previous government and facing presumably for some time what is an unfavourable opposition."
But, he added: "No prime minister has inherited a party as low in the polls as either Boris Johnson or Jeremy Hunt are going to do.
"They are inheriting what at the moment at least is a very sticky, very volatile wicket."