Theresa May on Wednesday will become the prime minister who leads Britain into talks to quit the European Union, after her last rival in the bid to succeed David Cameron pulled out.
May became the only contender after Andrea Leadsom -- who had stirred a storm for suggesting she was more qualified to be premier because she had children -- abruptly quit the race on Monday.
Cameron later announced May would take over from him on Wednesday, when he will to go to Queen Elizabeth II and tender his resignation after one final Prime Minister's Questions session in parliament.
"We'll have a new prime minister in that building behind me by Wednesday evening," he said in a statement outside 10 Downing Street.
Accompanied by her banker husband Philip and surrounded by supportive MPs, a smiling May later stressed the need "to negotiate the best deal for Britain in leaving the EU" in brief comments outside parliament.
Britain has faced the worst political turmoil in generations following June 23's shock vote to leave the European Union.
The outcome prompted Cameron to step down, plunging his Conservatives into a bitter leadership race.
At the same time, the head of the main opposition Labour party, Jeremy Corbyn, is also facing a challenge to his job.
Senior MP Angela Eagle formally launched her bid on Monday, and Labour's election coordinator, Jon Trickett, said the party should brace for general elections soon after May takes office.
"It is crucial, given the instability caused by the Brexit vote, that the country has a democratically-elected prime minister," said Trickett.
"I am now putting the whole of the party on a general election footing."
While May supported Britain staying in the EU, she cut a low profile during the referendum and insists she will honour the vote, stressing: "Brexit means Brexit".
"There will be no attempts to remain inside the EU, there will be no attempts to rejoin it by the back door, no second referendum," she said at a leadership campaign event before Leadsom pulled out.
She wants to begin formal talks to leave the EU by the end of the year at the earliest, despite pressure from Brussels to speed things up.
Jeroen Dijsselbloem, the Dutch finance minister who heads the Eurogroup of his 19 eurozone counterparts, restated calls for the transfer of power to take place as soon as possible.
"The sooner we can sort out -- let me say it diplomatically -- this problematic situation, the better," Dijsselbloem told reporters.
General election call
The pound, which hit a 31-year low following the Brexit vote, briefly rose after Leadsom, a pro-Brexit figure with no senior ministerial experience, withdrew from contention to be prime minister.
May, a 59-year-old clergyman's daughter, will be Britain's second female prime minister after Margaret Thatcher, who was in office from 1979-1990.
She has portrayed herself as the leader who can unite the country and a tough negotiator who can stand up to Brussels in what promises to be tortuous talks over Britain's exit from the 28-nation bloc.
Leadsom's withdrawal means all the ruling Conservative party's top Brexit campaigners -- Boris Johnson, Michael Gove and Leadsom as well as outgoing UK Independence Party leader Nigel Farage -- have now stepped back from leadership roles.
'Howl of pain'
On the latest in a string of recent astonishing days at Westminster, Eagle also launched her bid to take over the Labour leadership.
Corbyn, a veteran socialist supported by many grassroots members, has lost the confidence of at least three-quarters of his MPs, many of who accuse him of lacklustre campaigning to stay in the EU.
Eagle, who is from Labour's "soft" left and was the first female MP to enter a civil partnership with her female partner in 2008, said Britain faced "dangerous times".
Of the referendum, she added: "This vote was a message for millions in our country who felt that no-one had listened to them for a very long time".
"For many of them, it was a howl of pain."
By contrast with the Conservative outcome, there is still much uncertainty about how the Labour leadership contest will work.
Central to the race will be a decision by Labour's governing National Executive Committee (NEC) about whether Corbyn automatically gets on to the ballot or needs to secure 51 lawmakers' nominations, which he could struggle to do. The NEC is due to meet on Tuesday.