Cameron stepped down after Britons rejected his entreaties and voted to leave the EU in a referendum last month, severely undermining European efforts to forge greater unity and creating economic uncertainty across the 28-nation bloc.
May, 59 assumed office after an audience with Queen Elizabeth. An official photograph showed her curtseying and shaking hands with the smiling monarch, for whom she is the 13th prime minister in a line that started with Winston Churchill.
She is also Britain’s second female head of government after Margaret Thatcher.
She must try to limit the damage to British trade and investment as she renegotiates the country’s ties with its 27 EU partners. She will also attempt to unite a divided ruling Conservative party and a fractured nation in which many, on the evidence of the vote, feel angry with the political elite and left behind by the forces of globalization.
EU leaders, keen to move forward after the shock of ‘Brexit’, want May to launch formal divorce proceedings as soon as possible to help resolve the uncertainty.
But she has said the process should not be launched before the end of year, to give time for Britain to draw up its negotiating strategy.
Although she favored Britain remaining in Europe, May has repeatedly declared that “Brexit means Brexit” and that there can be no attempt to reverse the referendum outcome.
The shock vote partly reflected discontent with EU rules on freedom of movement that have contributed to record-high immigration – an issue on which May, as interior minister for the past six years, is politically vulnerable.
But EU leaders have made clear that free movement is a fundamental principle that goes hand-in-hand with access to the bloc’s tariff-free single market, a stance that will hugely complicate May’s task in hammering out new terms of trade.
“My advice to my successor, who is a brilliant negotiator, is that we should try to be as close to the European Union as we can be for the benefits of trade, cooperation and of security,” Cameron told parliament in his last appearance before resigning.
Appearing later in Downing Street with his wife Samantha and their three children, he delivered his parting remarks to the nation after six years dominated by the Europe question and the aftermath of the global financial crisis.
“It’s not been an easy journey and of course we’ve not got every decision right,” he said, “but I do believe that today our country is much stronger.”
In parliament, Cameron took the opportunity to trumpet his government’s achievements in generating one of the fastest growth rates among western economies, chopping the budget deficit, creating 2.5 million jobs and legalizing gay marriage.
Yet his legacy will be overshadowed by his failed referendum gamble, which he had hoped would keep Britain at the heart of a reformed EU.