Relatives of some of those who died when the Airbus A330 vanished in darkness and plunged into the Atlantic during a storm listened to the verdict in silence after a 17-year legal battle over responsibility for France's worst air disaster.
A lower court had in 2023 cleared the two French companies, both of which have repeatedly denied the charges.
Thursday's verdict is the latest milestone in a legal marathon involving relatives of the mainly French, Brazilian and German victims and two of France's most emblematic companies.
The appeals court ordered them both to pay the maximum fine for corporate manslaughter, 225,000 euro ($A366,500), following the request of prosecutors during last year's eight-week trial.
The fines, amounting to just a few minutes of either company's revenue, have been widely dismissed as a token penalty.
But family groups have said a conviction would represent a formal recognition of their plight.
French lawyers have predicted further appeals to the country's highest court, potentially dragging the process out for years more and prolonging the ordeal for relatives.
But the trial was seen as a cathartic moment for many relatives and turns the page on almost two decades of in-fighting within France's aviation establishment over the cause of the crash, which led to changes in training.
Any appeals following Thursday's verdict will shift the focus from the AF447 cockpit to the intricacies of law.
Relatives and lawyers sat in a high-windowed courtroom as a judge read out a list of victims, many sharing the same family names.
Flight AF447 vanished from radar screens on June 1, 2009, with people from 33 nationalities on board.
The plane's black boxes were recovered two years later after a deep-sea search.
In 2012, BEA crash investigators found the plane's crew had pushed their jet into a stall, chopping lift from under the wings, after mishandling a problem to do with iced-up sensors.
Prosecutors, however, focused their attention on alleged failures inside both the plane maker and airline.
Those included poor training and failing to follow up on earlier incidents.
To prove manslaughter, prosecutors had to not only establish that the companies were guilty of negligence but also pull the threads together to demonstrate how this caused the crash.
