Prince Harry surprised keen racegoers as they took part in the annual 26.2 mile trek across the city.
Everyone from professional athletes to runners dressed as clowns and Big Ben are taking part in the famous race – raising millions for charities.
Kenya’s Eliud Kipchoge ran the second fastest marathon in history to win the event for a fourth time as Britain’s Mo Farah finished fifth.
“No other mass participation event comes anywhere near this kind of fundraising”
Kipchoge, 34, who broke the world record in Berlin last year, triumphed in two hours two minutes 38 seconds.
Farah finished 3mins 1sec behind Kipchoge, while Briton Callum Hawkins was 10th.
Kenya’s Brigid Kosgei, 25, became the youngest female London winner, with Britain’s Charlotte Purdue 10th.
Away from the professionals, more than 40,000 runners put themselves through the gruelling spectacle as thousands of Londoners cheered them on.
Dozens of celebrities also took part in a bid to raise as much cash for good causes as possible.
Chris Evans, Ed Gamble and Kirsty Gallagher took to to the streets along with eight Eastenders stars who are fundraising in memory of the legendary Barbara Windsor.
It is expected this year’s race will take the total of London Marathon fundraising past the £1 billion mark.
Official figures from Virgin Money London Marathon say that the event has raised more than £955m since it first took place in 1981.
Event director Hugh Brashner said: “No other mass participation event comes anywhere near this kind of fundraising.”
The race has enjoyed dry weather despite the threat from Storm Hannah.
Sir Andy Murray kicked off proceedings this morning as runners took to the streets in Blackheath, south east London, making their way towards the Mall close to Buckingham Palace.