LONDON — Prime Minister Boris Johnson and his Conservative Party won a commanding majority in the British Parliament, a striking victory that redraws the lines in British politics and paves the way for the country’s exit from the European Union early next year.

The Conservatives were projected to win 363 seats in the House of Commons, versus 203 for the Labour Party, according to the BBC’s projections, with almost all of Parliament’s seats decided. That would give the Conservatives about a 75-seat majority, their largest since that amassed by Margaret Thatcher in 1987.

As the results flowed in from individual districts, they pointed to a radical reconfiguration of Britain’s political map. The Conservative Party was winning dozens of Labour seats in the industrial north and Midlands, shattering the so-called red wall that has undergirded the Labour Party for generations.

For Johnson, whose brief tenure has been marked by serial defeats in Parliament, legal reversals and ceaseless upheaval, it was a resounding vindication. Defying predictions that he would be tossed out of his job, the prime minister is assured of leading Britain through its most momentous transition since World War II.

For Britain, which has lurched from crisis to crisis since the 2016 Brexit referendum, its future seemingly shrouded in perpetual uncertainty, the election provided a rare moment of piercing clarity.

“It’s a remarkable victory,” said Tony Travers, a professor of politics at the London School of Economics. “Boris Johnson now has five years in power. Brexit will happen. Labour faces an existential question about its future — yet again.”

As news of the Conservative victory began to circulate, the pound surged in trading against the dollar and euro, reflecting relief that British politics is likely to stabilize and Britain is more likely to have an orderly departure from the European Union.

While the preelection polls had been predicting a Conservative victory, the news for the party Thursday was even better than had been forecast, with the Tories projected to gain about 50 seats, in excess of what most projections. The Labour Party was set to lose about 60 seats, its worst showing since 1983, and one that seemed likely to lead to the resignation of the party’s leader, Jeremy Corbyn.