Rishi Sunak was all set to become Britain's first prime minister of color after the other candidates quit the race to lead the Conservative Party on Monday.
It now leaves him with the task of steering a deeply divided country through an economic downturn set to leave millions of people poorer.
Sunak, one of the wealthiest politicians in Westminster, will be asked to form a government by King Charles, replacing Liz Truss, the outgoing leader who only lasted 44 days in the job.
He defeated centrist politician Penny Mordaunt, who failed to get enough backing from lawmakers to enter the ballot, while his rival, the former prime minister Boris Johnson, withdrew from the contest saying he could no longer unite the party.
"This decision is an historic one and shows, once again, the diversity and talent of our party. Rishi has my full support," Mordaunt said in a statement as she withdrew from the race just minutes before the winner was due to be announced.
The pound and British government bond prices jumped briefly on news of Mordaunt's withdrawal but soon returned to their previous levels.
Sunak, the 42-year-old former finance minister, becomes Britain's third prime minister in less than two months, tasked with restoring stability to a country reeling from years of political and economic turmoil.
The multi-millionaire former hedge fund boss would be expected to launch deep spending cuts to try to rebuild Britain's fiscal reputation, just as the country slides into a recession, dragged down by the surging cost of energy and food.
Britain has been locked in a state of perma-crisis ever since it voted in 2016 to leave the European Union, unleashing a battle at Westminster over the future of the country that remains unresolved to this today.
The latest bout of drama has drawn dismay in foreign capitals and ridicule from the world's press.
Sunak came to national attention when, aged 39, he became finance minister under Johnson just as the COVID-19 pandemic hit Britain, developing the successful furlough scheme.
The former Goldman Sachs analyst will be the United Kingdom's first prime minister of Indian origin.
His family migrated to Britain in the 1960s, a period when many people from Britain's former colonies moved to the country to help it rebuild after the Second World War.
After graduating from Oxford University, he went to Stanford University where he met his wife Akshata Murthy, whose father is Indian billionaire N. R. Narayana Murthy, founder of outsourcing giant Infosys Ltd.
