The man, in his 50s, was found dead in a sleeping bag on Wednesday afternoon and was believed to have been dead for at least three days.
Many London taxi drivers have struggled to make a living during the pandemic due to limits on international travel.
According to The Daily Mail, drivers could be seen sleeping inside their cabs – with some placing mattresses in the back of their vehicles.
If they leave their cabs in the line and go home to rest for a few hours they will lose out on the prospect of picking up a passenger from the terminal.
One cabbie told the paper: “Everyone has been affected by the pandemic but fewer flights obviously means fewer fares so we are waiting longer.
“There are fewer fares but what do you do, just sit indoors twiddling your thumbs or come out and work?”
A Scotland Yard spokesperson said: “Police were called shortly after 16:01hrs on Wednesday, 12 May to Newall Road, near Heathrow following reports of an unresponsive man in a car.
“Officers and London Ambulance Service attended and a man in his 50s was pronounced dead at the scene. The death is not being treated as suspicious and a file will be prepared for the coroner.’
A Heathrow Airport spokesperson said: “We are aware of and saddened by this incident. Our teams are on hand to support with any police enquiries.”