Club owner Robert Louis-Dreyfus received a three-year suspended sentence, according to the verdicts read out in the court.
The men were also fined 375,000 euros ($480,800) each. Lawyers for both said they would appeal.
Prosecutors said some 22 million euros ($28.21 million) were illegally diverted from club funds as part of the transfer of 15 players between 1997 and 1999 -- including France 1998 World Cup winners Laurent Blanc and Christophe Dugarry.
"Fraud was one of the tools of the OM management between 1997 and 1999," judge Vincent Turbeaux told the court on Friday. "This created a disastrous image of professional football."
The ruling, coming only hours before the World Cup kicks off in Germany, was another reminder of the seamy side of the game. Italy is also in the throes of a match-fixing scandal.
During the trial, which began in March after a six-year investigation, the court heard of a complicated system of international cash transfers between several tax havens as part of a system of hidden commissions paid on player moves.
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"For the moment, it doesn't change anything for the love he has for his club and his desire to keep it going," Sophie Bottai told Reuters. "There will be no change, although in the end it will be his personal decision," she said.
Prosecutors had demanded a two-year jail term for Courbis and a suspended term of three to four years for Louis-Dreyfus who was not present in court on Friday.
During the trial, which began in March, Courbis admitted he was paid four million French francs ($100,000) in a Swiss bank account but he denied any wrongdoing.
On Friday he said there had been "an attempt to exterminate me in the world of football."
Louis-Dreyfus insisted that until the trial he knew nothing about widespread fraud at the club but he admitted that the court proceedings had revealed extensive wrongdoing which he said had deeply upset him.