The 21-year-old former Le Havre junior, joined City’s academy in 2012.
He made the step up to the senior side in 2015 but was loaned out to Genoa, where he has spent the past two seasons, scoring three goals in 37 Serie A ties.
Now he has completed a move to the Scottish Premier League on a four-year deal, for a fee thought to be around £4.5m.
Speaking to the club’s official website, he said: “I’m most looking forward to the derby and playing in the Champions League.
“I remember them beating Barcelona five years ago in the group stages. Not every club gets to play in this competition so I’m happy to have the chance to play there with Celtic.
“Celtic is a fresh challenge for me. While Genoa are a good team, I knew they wouldn’t win Serie A as they were not a top team like Juventus, but I know Celtic are a big team in Scotland.”