Other travellers became aware of the emergency when a dark-haired passenger, who appeared to be on his own, would not wake up.
A defibrillator was used to try to resuscitate the passenger, but it was not successful.
The flight left Paphos Airport at about 12.20pm GMT and concerns for the man's health were sparked at about 3.40pm.
EasyJet cabin crew asked if there was a doctor or a paramedic on board but no one was able to offer more than the cabin crew's first aid knowledge, the Daily Star reported.
The captain confirmed that there had been a "medical incident" and asked everyone to treat the dead man with dignity as the plane passed over Paris at about 4.30pm.
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Passengers were held when they landed at Gatwick while paramedics boarded the plane and pronounced the man dead.
An anonymous passenger praised the way in which the easyJet crew dealt with the incident, telling the Daily Star: "The team handled the situation with extraordinary composure and professionalism."
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"EasyJet can confirm that, sadly, a passenger died onboard flight EZY8454 from Paphos to London Gatwick on November 17," the airline said.
"The well-being of our passengers and crew is always easyJet's highest priority.
"Our crew are trained to respond to medical issues and did all possible during the flight.
"Our thoughts are with the family and friends of the customer and we are offering support and assistance at this difficult time."