LONDON — Prime Minister Theresa May of Britain, smarting from a humbling snap-election defeat that cost her Conservative Party its governing majority, said on Friday that her party would stay in power by forming a minority government with the Democratic Unionist Party of Northern Ireland.

“What the country needs more than ever is certainty, and having secured the largest number of votes and the greatest number of seats in the general election, it is clear that only the Conservative and Unionist Party has the legitimacy and the ability to provide that certainty, by commanding a majority in the House of Commons,” Mrs. May said outside No. 10 Downing Street, using the full name of her party. “As we do, we will continue to work with our friends and allies, in the Democratic Unionist Party in particular.”

Mrs. May had called an election three years early in the hope of winning a stronger mandate as Britain prepares for two years of negotiations over its withdrawal from the European Union, but voters did not reward that gamble. Instead, they produced a hung Parliament — one in which no party has an outright majority in the 650-seat House of Commons.

The fractured voting — which saw strong gains by the largest opposition party, Labour, and modest gains by a smaller party, the centrist Liberal Democrats — was a further indication of stark political divisions in Britain, days before formal negotiations over withdrawal from the European Union are scheduled to begin in Brussels.