PICTURED: Dramatic images of spectacular lightning over YorkshireAn exhausted Sir Mo broke the marathon record by a British athlete as he finished third in the men's race, despite an initial 11-second discrepancy between the two official times.
The 35-year-old multiple Olympic and world gold medallist struggled with the pace, the hot conditions and mix-ups over water bottles, but he still beat Steve Jones' 33-year-old record with a time - ratified more than an hour after crossing the finishing line - of two hours, six minutes and 21 seconds.
Race organisers had previously urged runners to reconsider aiming for personal bests and suggested ditching the fancy dress costumes amid the unseasonably warm April weather.
It would go on to be the warmest London Marathon on record, with the Met Office posting highs of 23.2C (73.8F) - beating the previous best of 22.7C (72.8F) set in 1996.
Elsewhere on the track, six-time Paralympic gold medallist Weir won the men's wheelchair race for an unprecedented eighth time.
READ: Review of ‘crucial’ flood alert systemSir Mo said he would spend time with his family after not seeing his children due to a strict training regime in Ethiopia during the last three months.
He said: "It slowed down after halfway, from there you pay the price, you can't go off that fast and come away with 2.02.
"It was a hard way to run the pace because we were set for the world record pace at the beginning...
"I know I can go at least 2.04, 2.05, in an even-paced race, today it was the hardest way to run in any race. But at the end of the day you've got to fight like a man."
Eliud Kipchoge of Kenya won the men's race in a time of two hours, four minutes and 16 seconds, while compatriot Vivian Cheruiyot won the women's race in a time of two hours, 18 minutes and 31 seconds.
Those not competing in the elite races received a royal send-off as the Queen pushed the event's start button, sending thousands of competitors pounding 26.2 miles through the capital's streets.
More than 40,000 marathon runners then proceeded to follow hot on their heels.
Among this year's runners were firefighters who tackled the Grenfell Tower blaze, a police officer stabbed in the London Bridge terror attack and members of the Stephen Lawrence Charitable Trust.
Meanwhile, almost 100 runners lined up to attempt Guinness World Records - dressed variously in suits of armour, as mythical creatures and wearing stilts and ski boots.
Last year, the event raised £61.5 million for charity, a world record for an annual one-day fundraising event, making the total raised since 1981 around £890 million, organisers said.
A record 386,050 people applied for this year's race - almost a third more than last year and the highest number for any marathon in the world.