Polls put Labour candidate Khan, 45 and his Conservative rival Zac Goldsmith, 41, as the top two candidates in a field of 12.
– Sadiq Khan –
Khan’s rise to prominence represents a modern fairytale.
Born in London in 1970 to parents who had recently arrived from Pakistan, he grew up in public housing with his six brothers and sister in Tooting, an ethnically diverse residential area in the south of the city.
But his modest background plays well in a city that boasts about its diversity and loves a self-made success story.
Khan regularly recalls how his father drove London’s famous red buses, how his mother was a seamstress and one of his brothers is a motor mechanic.
At school, he wanted to study science and become a dentist. But one of his teachers spotted his gift for verbal sparring and directed him towards law.
He became a lawyer specialising in human rights, and spent three years at the human rights campaign group Liberty.
He is also handy at actual sparring, having learnt how to box to defend himself in the streets against those who hurled racial slurs at him.
Aged 15, he joined the Labour Party and he became a councillor in the mainly-Conservative Wandsworth local borough in 1994, a post he held until 2006.
In 2005 he gave up his legal career on becoming the member of parliament for Tooting, where he still lives, with his lawyer wife Saadiya and their two daughters.
Prime minister Gordon Brown made him the communities minister in 2008 and he later served as Britain’s transport minister, becoming the first Muslim minister to attend Cabinet.
While Conservatives try to establish links between him and Islamic extremists, he points out that he voted for gay marriage — which earned him death threats — and he has always denounced radicalism as a cancer.
Khan told The Daily Telegraph newspaper he wants “to be there for all Londoners — for those of every faith, for millionaires, billionaires, bus drivers and junior doctors”.
– Zac Goldsmith –
Goldsmith has his own sort of fairytale to tell: extremely rich, handsome, impeccably well-dressed and educated at the elite Eton College.
However, those are not necessarily qualities which make a candidate seem close to voters and their everyday concerns.
During the election campaign he also struggled with some straightforward London questions thrown at him by the BBC: the names of football stadiums and stops on the Underground plus the location of museums.
He is the son of the late tycoon financier Jimmy Goldsmith — who left his family £1.2 billion ($1.75 billion, 1.5 billion euros) — and first surfaced in the newspaper society columns with his sister Jemima, ex-wife of the Pakistani cricket star Imran Khan.
He was expelled from Eton at 16 for having cannabis in his room, though he insists it was one of the few times at school when he was actually innocent.
Goldsmith went travelling instead of heading to university and ended up editing his uncle’s magazine, The Ecologist.
He became the MP for his local Richmond Park area of plush west London in 2010. He regularly refuses to toe the party line, voting against the government.
Married for the second time to heiress Alice Rothschild, he is a father-of-five.
To those who question his lack of experience, his campaign manager Nick de Bois said it was better to judge him on his actions, and points out that he had the biggest increase in majority of any MP at the 2015 general election.
It would also be better for London to have a mayor who could work with a Conservative government, he added.
Affable, polite and softly-spoken, Goldsmith sometimes struggles to get across his passion for politics on the stump, leading some newspapers to dub him “Sleeping Beauty”.