Liz Truss will become the next prime minister after defeating Rishi Sunak in the Conservative Party leadership contest.
Ms Truss, who was the favourite to win, will succeed Boris Johnson on Tuesday and become the nation's third female leader.
The foreign secretary used her victory speech to indicate she would not trigger an early general election, instead pledging to secure "a great victory for the Conservative Party in 2024".
She won by a comfortable margin, but her victory was slimmer than in other recent leadership contests.
Ms Truss said it is an "honour to be elected" as she thanked her party for organising "one of the longest job interviews in history".
In a short speech after the result was announced, she issued her thanks to her "friend" Mr Johnson.
"You got Brexit done. You crushed Jeremy Corbyn. You rolled out the vaccine and you stood up to Vladimir Putin," she said.
Mr Johnson, who was forced to resign after a wave of ministers left his government over a series of controversies, will visit the Queen at Balmoral to formally tender his resignation tomorrow.
Reacting to Ms Truss' victory, he said his successor "has the right plan to tackle the cost of living crisis, unite our party and continue the great work of uniting and levelling up our country".
Mr Sunak, the former chancellor, has also called for the Conservative Party to unite behind Ms Truss following his loss.
In a tweet he said: "Thank you to everyone who voted for me in this campaign. I've said throughout that the Conservatives are one family.
"It's right we now unite behind the new PM, Liz Truss, as she steers the country through difficult times."
Ms Truss will officially become PM tomorrow when she will meet the Queen, who will invite her to form a government.
She is expected to make a speech outside Number 10 once she takes office and will then get to work on appointing her cabinet.