The plane was diverted to Morocco and emergency services called in but nothing could be done to save the passenger.
The incident happened on Monday when Jorge Barbosa, described by newspaper Correio da Manhã (CM) as being in his 40s, died of a suspected heart attack while on the flight between Angola and Portugal after feeling unwell.
Family and friends are now reportedly demanding answers as to how and why the man died so suddenly.
His body has been sent for autopsy to determine the cause of death.
Jorge Barbosa had been working in Luanda for a number of years and, according to reports, was looking forward to spending some time on holiday in Portugal with family and friends.
An official source for TAP confirmed to CM that the plane had to make an emergency landing in Agadir, Morocco, “due to a medical emergency” and that “all the usual procedures required in such urgent cases were respected.”
The flight reached Lisbon with a delay of around five hours.
In related news a Ryanair flight from Porto to Lille, France, was forced to make an unplanned landing in Nantes after a passenger became unwell on the plane.
In a statement the airline confirmed “the flight diverted to Nantes after a passenger fell ill on board.”
The statement stressed that “the aircraft landed normally and the passenger was assisted by medical personnel in Nantes.”