The horrific impact left a crater in the lawn and smashed a concrete path.
Startled neighbours heard a loud bang – described by one as a “whomp” – as the suspected migrant’s body landed in the small garden in Clapham, south London.
The unidentified stowaway, who was wearing a blue T-shirt and denim jeans, landed face down very close to the sunbather, named locally as John Baldock.
It is believed the man was already dead, and one neighbour has told how the body was frozen when it narrowly missed hitting the sunbather.
The stowaway was hidden within a Kenya Airways plane that was flying over the capital on its final approach to Heathrow Airport.
His body plunged from a landing gear compartment as the plane lowered its wheels.
A plane spotter, who was following the nine-hour flight on an app from Clapham Common, had seen the body fall and arrived at the scene at around the same time as police.
Neighbours said the sunbather was lucky not to be killed.
Witnesses said Mr Baldock was in shock after the stowaway nearly landed on top of him.
One of the Mr Baldock’s friends told the Sun: “He was so lucky not to be hit and killed. The impact obliterated the body.”
The plane, which took off from Jomo Kenyatta International Airport in Nairobi, landed at Heathrow at 3.50pm, just over ten minutes after police were called.
He would have had to survive almost nine hours starved of oxygen and temperatures of around -60C at an altitude of 40,000ft.
Kenya Airways called the death “unfortunate” and said it was cooperating with British and Kenyan authorities.
On inspecting the aircraft police found a bag containing food and clothing at the rear left landing gear.
A spokesperson for the airline, which is Kenya’s flag carrier, said: “The incident has been treated as a sudden death and is now a police matter.
“The police have already been in contact with the Kenya High Commission to help identify and name the person.”