Mohamed Lahouaiej Bouhlel, a 31-year-old Tunisian, rammed a 19-tonne lorry into revellers enjoying a July 14 fireworks display on Nice's seafront Promenade des Anglais before he was shot dead by police.
The attack, claimed by the Islamic State group, left 434 people injured.
Nice's Pasteur hospital said the man who died Thursday had been on life support since the day of the attack.
Local newspaper Le Messager said he was a 56-year-old from France's eastern Haute-Savoie region, whose wife and son were also killed in the attack and whose 14-year-old daughter remains in hospital.
President Francois Hollande is facing mounting demands to improve security after a string of jihadist attacks, dating back to January 2015, when gunmen stormed the offices of Charlie Hebdo satirical magazine and a Jewish store.
Then in November, 130 people were killed at restaurants, bars and a concert hall in Paris.