Boris Johnson’s ex-chancellor, 42, won the support of fellow MPs and will take the helm without the need for a vote from the party membership.
Exactly when he will officially start and take over from Liz Truss is unclear at the time of writing.
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Sunak is expected to deliver a speech to Tory MPs, who have been at war with one another over the last few weeks, at 2.30pm on Monday.
The only other candidate who formally declared that they were running to become PM was Penny Mordaunt, though she pulled out of the race at the last minute, paving the way for Sunak’s victory.
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“These are unprecedented times. Despite the compressed timetable for the leadership contest it is clear that colleagues feel we need certainty today. They have taken this decision in good faith for the good of the country.
“Members should know that this proposition has been fairly and thoroughly tested by the agreed 1922 process.
“As a result, we have now chosen our next Prime Minister. This decision is a historic one and shows, once again, the diversity and talent of our party. Rishi has my full support.
“I am proud of the campaign we ran and grateful to all those, across all sides of the party, who gave me their backing.
“We all owe it to the country, to each other and to Rishi to unite and work together for the good of the nation. There is much work to be done.”
— Penny Mordaunt (@PennyMordaunt) October 24, 2022
Sunak and Mordaunt both had to win the support of 100 MPs, and while Sunak reached the total easily, it is understood that Mordaunt fell just short with 90.
Former PM Boris Johnson dropped out of the race on Sunday, despite rumours that he privately claimed to have had enough support.
The announcement marks a whirlwind return for Sunak, who was beaten in the previous contest in September by Liz Truss.
Sunak is the youngest PM of modern times and will be the first Hindu PM.
Earlier on Monday, Labour deputy leader, Angela Rayner, said: “Tory MPs are set to hand Rishi Sunak the keys to No 10 without him saying a single word about how he’d govern.
“Little wonder he’s dodging scrutiny: he’s so dire that just a few weeks ago he was trounced by Liz Truss.
“No mandate. No one voted for this.”
Liberal Democrat leader Ed Davey said the Tories have ‘installed another out-of-touch’ Prime Minister, commenting: “The only way to end the chaos is a general election now.”
Sunak does not have to hold a general election until January 2025 at the latest, despite pressure to do so from opposition parties.
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