His triumph completed the double for Kenya after Mary Keitany sealed her third London title in a women only world record of 2:17.01, beating Britain's Paula Radcliffe's previous best by 41 seconds.
The IAAF recognises two marathon world records for women, one for "mixed gender" races and the other for "women only" races.
Tirunesh Dibaba of Ethiopia finished Sunday's race 56 seconds adrift in second place, while Aselefech Mergia of Ethiopia was third.
Simbu, victor of the 2017 Mumbai Marathon and fifth-placed at last year's Commonwealth Games, produced his best 42km race ever as he posted a new personal best time of 2:9:10 hours. She becomes the fastest women to cross the line in a "Women Only" Elite marathon. The record 40,000 runners were cheered on by over 800,000 spectators on the streets of London and were even given a Royal sendoff with Princes William and Harry sending them on their way.
"I've been preparing to win this race since Christmas so I'm very grateful that I achieved my goal".
She said: "I didn't want the marathon training to affect my normal life".
"I thought I would run 2:17:59 or something, so to run 2:17:01 is awesome".
Police have ramped up security for tomorrow's London Marathon in the wake of the Westminster terror attack.
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Earlier, Britain's six time Paralympic champion David Weir took victory in the men's wheelchair race, beating his rival and last year's victor Marcel Hug in a sprint finish.
"Seeing the effect the cancer had on her and how she deteriorated during those two years was really hard".
"To get in my training I've been going out at 3am or 4am for runs".
Sam Watts (above), 35, running the London Marathon this year on behalf of Pancreatic Cancer UK.
She continued: "I dedicate each mile to someone or something that I love during marathons but I always keep the last mile for my dad". I think the course has changed a little bit and it felt better than before. "My expectation was to win because I prepared very well in Kenya and my training went ideal".
It followed him being dropped early on by the lead group containing Kenya's Bedan Karoki and Abel Kirui, Ethiopia's Olympic silver medallist Feyisa Lilesa, Ghirmay Ghebreslassie and Wanjiru.
The pair crossed the line at the same time (02:51:08), and Rees took some deserved acclaim on Twitter.
The 43-year-old is also running in memory of his late wife Elizabeth, who died of terminal cancer last year.