The court in the southern city of Aix-en-Provence upheld a previous ruling ordering the airline to pay 8.1 million euros in damages and 200,000 euros in fines for breaching French labour law.
In October 2013 the airline was found guilty of avoiding payroll and other taxes, as well as preventing workplace councils from functioning and hampering employees' access to unions.
Ryanair appealed the ruling in June 2014.
The airline will have to pay damages to trade unions, France's social security system and pilots among others.
Ryanair had based four planes and 127 employees at the Marseille-Marignane airport between 2007 and 2010 without applying French labour law or filling out tax declarations in France.
The company argued that it did not have a permanent base in the area and that it was entitled to keep its workforce on Irish contracts.
But prosecutors said its claim was not credible because the workers were living locally and the airline had offices there.