The 45-year-old, a former human rights lawyer and an opposition Labour lawmaker, was swept into City Hall on 57 per cent of the vote, becoming the first Muslim mayor of a Western capital in the process.
After bitter campaign: Sadiq Khan becomes first Muslim mayor of London
After a campaign that saw his main rival try to establish links between Khan and religious extremists, the mayor now faces the task of bringing London's diverse communities together to keep it on its perch as a top world city.
In his acceptance speech, Khan promised to be a "mayor for all Londoners" and said his late father, who emigrated from Pakistan in the 1960s, would be "so proud".
"I never dreamed that someone like me could be elected as mayor of London. And I want to say thank you to every single Londoner for making the impossible possible today," he said.
He promised to work to provide more affordable housing and transport, to reduce pollution and encourage more and better paid jobs.
"I want every single Londoner to get the opportunities that our city gave to me and to my family, the opportunity not just to survive but to thrive," he said.
Khan's journey to City Hall is like a modern fairytale.
Born in London in 1970 to parents who had recently arrived from Pakistan, Khan was the fifth child out of seven brothers and one sister.
He grew up in public housing in Tooting, an ethnically mixed residential area in south London, and slept in a bunkbed until he was 24.
His modest background plays well in a city that is proud of its diversity and loves a self-made success story.
Khan regularly recalls how his father drove one of London's famous red buses, and his mother was a seamstress. One of his brothers is a motor mechanic.
London set to elect Muslim mayor
He is a handy boxer, having learnt the sport to defend himself in the streets against those who hurled racist abuse at him, and two of his brothers are boxing coaches. He also ran the London Marathon in 2014.
At school, he wanted to study science and become a dentist. But a teacher spotted his gift for verbal sparring and directed him towards law.
He gained a law degree from the University of North London and started out as a trainee lawyer in 1994 at the Christian Fisher legal firm, where he was eventually made a partner.
He specialised in human rights, and spent three years chairing the civil liberties campaign group Liberty.
He represented Louis Farrakhan, leader of the Nation of Islam movement, and Babar Ahmad, a mosque acquaintance who was jailed in the United States after admitting providing support to the Taliban regime in Afghanistan.
Khan joined the Labour Party aged 15 when Conservative prime minister Margaret Thatcher was in her pomp.
He came a local councillor for Tooting in the Conservative-dominated Wandsworth local borough in 1994, and its member of parliament in the 2005.
Sadiq Khan nears winning London mayoral polls
He still lives in the area with his lawyer wife Saadiya and their two teenage daughters.
Prime minister Gordon Brown made him the communities minister in 2008 and he later served as transport minister, becoming the first Muslim minister to attend cabinet meetings.
In parliament, he voted for gay marriage -- which earned him death threats.
His London mayoral election campaign focused on providing affordable homes for Londoners and freezing transport fares.
Khan is London's third mayor after Labour's Ken Livingstone (2000-2008) and Conservative Boris Johnson (2008-2016).
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