Pilot Pascal Fauret, co-pilot Bruno Odos, passenger Nicolas Pisapia and alleged broker Alain Castany were arrested in March 2013 aboard a Dassault Falcon 50 jet with 26 suitcases carrying 680 kilograms of cocaine, Dominican authorities say.
The group was about to take off from the Caribbean resort of Punta Cana.
After fifteen months of detention, they were released on 21 June 2014. But on Friday, after 10 hours of deliberation, a court found them "guilty of the crime of associating to (...) possess illegal drugs", read the tribunal secretary.
The Frenchmen have protested their innocence and say they did not know the drugs were on the plane. But a Dominican judge rejected the argument, saying that the pilots were responsible for what was on board their flight.
The lawyer for the pilots, Maria Elena Gratereaux, told reporters after the sentencing that she would appeal.
Since their arrest, their court hearings had been postponed time and again, which French Foreign Affairs Minister Laurent Fabius described at one point as “very shocking”.
Of the 10 Dominicans charged with complicity in the case, six were acquitted and four others given sentences ranging from five to 10 years in prison.