The 33-year-old, who trained with his new teammates today, will wear the number 10 shirt after Mickael Le Bihan agreed to vacate it for the Dutchman.
A statement from Nice read: "It's now official. OGC Nice's 2017-18 squad now has a third UEFA Champions League winner in it. After Dante and Mario Balotelli, former European champion Wesley Sneijder will also wear the red-and-black shirt this season after passing a medical on Monday.
"He also knows which shirt he'll be wearing this season. Mika Le Bihan respectfully agreed to 'give up' the number 10 he had been wearing it to present it to the new arrival in the dressing room."
Sneijder, who has previously played for Ajax, Real Madrid and Inter Milan, made 174 appearances and scored 45 goals during his five-year spell at Galatasaray.