Meet Theresa May, the new Britain Prime Minister To Be.

The topsy-turvy politics of Britain’s endlessly unpredictable summer took another stunning twist on Monday, with the selection by default of a prime minister who had advocated staying in the European Union but will now come under immediate pressure to fulfill her promise to lead the nation’s exit.

Theresa May, the hard-charging home affairs secretary, was elevated to Britain’s top job when the woman who was to spend the summer campaigning against her, Energy Minister Andrea Leadsom, preemptively dropped out of the contest to succeed outgoing leader David Cameron.

With only one candidate left in the race, the 59-year-old May was named the winner by acclaim, a decision met with table-thumping approval by her fellow Tories in Parliament. She will take the keys to 10 Downing Street on Wednesday, once Cameron has had a final turn in the weekly political combat session known as Prime Minister’s Questions.

By coalescing around May, her Conservative Party avoided what could have been a bruising months-long campaign that threatened to inflame the still-raw wounds of last month’s E.U. referendum.

But the move is also likely to accelerate the pressure on Britain to exit the E.U. European leaders have said Britain must act as quickly as possible to get out, as have Leadsom and other British advocates for a geopolitics-rattling divorce known as Brexit.

What you need to know about Theresa May, Britain's next prime minister  Play
On Wednesday, Theresa May will become Britain’s next prime minister. She'll become the second female British prime minister after Margaret Thatcher.

Here's what you need to know her in 60 seconds.
May campaigned — if only barely — for the country to stay inside the E.U. But after the “leave” campaign won last month’s referendum and forced the pro-“remain” Cameron from office, May pivoted and said she would back an exit — a stance she reiterated in her victory speech.

“Brexit means Brexit, and we are going to make a success of it,” she said Monday afternoon as she stood in front of the gothic towers of Westminster and flashed a smile that is seldom seen on a politician known for her no-nonsense demeanor.

May will become the country’s 76th prime minister, but only the second woman to hold the job following Margaret Thatcher, who stepped down over a quarter-century ago.

Although May has been occasionally likened to Thatcher — Britain’s Iron Lady — she has lately been compared to a more contemporary leader: German Chancellor Angela Merkel.

Both May and Merkel were born in the 1950s, the daughters of church pastors. They both inhabit the center-right of European politics but are also known for a strong pragmatic streak.

Both are also considered tough negotiators — skills they’ll be putting to use against one another as May seeks a divorce deal with her soon-to-be-former E.U. counterparts.

The key question now is when she triggers the start of those talks. She had earlier said she did not want to invoke Article 50 — the never-before-used mechanism for exiting the E.U. — until at least 2017.

Her reluctance to move faster has sparked speculation that she might try to find a way to avoid Brexit — a possibility she emphatically rejected Monday, saying that there would be “no attempts to remain inside the E.U., no attempts to rejoin it by the back door, and no second referendum.”

Monday’s events make it less likely that she can go back on that pledge, even if she wants to. In dropping out of the race, Leadsom emphasized that she was trying to clear a path for her erstwhile rival to get on with the business of Brexit.