The Airbus A330 vanished from radars during a storm, with its wreckage found after a long search of 10,000 sq km (3,860 sq miles) of sea floor.
The black box was found after months of deep-sea searches in 2011.
All 12 crew members and 216 passengers on board the flight were killed when the plane crashed into the sea from a height of 38,000ft (11,580m), making it the deadliest incident in French aviation history.
Relatives of some of the passengers, which included mainly French, Brazilian and German nationals, gathered to hear the verdict on Wednesday.
The companies have been asked to pay the maximum fine, €225,000 ($261,720; £194,500) each – but some of the victims’ families have criticised the amount as a token penalty.
