LONDON -- She is a quiet, determined vicar's daughter who rose to the heights of British political power by outmanoeuvring better known, more outspoken men.

The favourites in a 2016 Conservative Party leadership competiton were Boris Johnson and Michael Gove. The winner was Theresa May, who became prime minister on a difficult mission to deliver Brexit.

May, 62, became prime minister after Britain's shock June 2016 vote to leave the EU toppled Prime Minister David Cameron, who had called the referendum and then argued for remaining in the bloc in a bid to squelch a long-running party squabble. And she has spent her entire premiership trying to deliver on the voters' decision.

Before the referendum, May had backed remaining in the EU bloc, but she has become one of the staunchest advocates of Brexit. "Brexit means Brexit" became her mantra -- a meaningless one, according to her detractors.

For a time, May was able to unite the warring factions of her party, which for decades has been divided over policy toward Europe. But her authority was severely dented when she gambled in April 2017 by calling a snap election in hopes of strengthening her hand in divorce negotiations with the EU -- only to lose her majority in Parliament.

May kept her government going by cobbling together a deal with the small Democratic Unionist Party of Northern Ireland, which is now threatening to withdraw its support because of opposition to her Brexit deal. The party's rejection of her deal will leave May's government in a perilous position even if she survives the no-confidence vote.

Much of May's Conservative Party also hates the agreement, struck after a year and a half of tough negotiations between Britain and the EU.

The pro-Brexit wing of the party says it gives too much away and will leave Britain bound to EU rules after it leaves. Pro-EU Conservatives criticize May for ruling out a softer Brexit in which Britain remains in the EU's single market and customs union.

May vowed that she would "see this through" and secure Parliament's backing for her deal. She came close to losing it all on Wednesday after angry Conservative lawmakers called for a no-confidence vote in Parliament. But she won it, 200 votes to 117.

Few doubt her fortitude and commitment to an idea of public service instilled in her upbringing as the daughter of an Anglican vicar.

May was first elected to Parliament in 1997, and soon established a reputation for unflashy competence and a knack for vanquishing her rivals.

She served for six years in the notoriously thankless job of home secretary, responsible for borders, immigration and law and order. In 2016 she beat flashier and better-known politicians, including flamboyant Brexit-backer Johnson, to the post of prime minister.

But her fabled stubbornness alone may not be enough.

As Britain's second female prime minister, May is inevitably compared to the first, Margaret Thatcher, whose steely determination May admires.

In November 1990, Thatcher faced a leadership challenge from Conservative rivals. She won the ballot, but not by enough to avoid a second-round vote.

"I shall fight on," Thatcher said defiantly. "I fight to win."

Within a week, she had been replaced.