Wilson, who left the City Ground for the Hoops in 2011, has been handed a three-year deal at the City Ground.
The 27-year-old defender won two SPL titles and a Scottish Cup winner's medal during his time at Celtic Park and he is raring to get going back at Forest.
He told the club's website: "It's nice to be back. I'm delighted to get it all sorted and I can't wait to get started to be honest.
"I wouldn't have left Celtic for just anyone, it had to be the right club. And no club fitted the bill better than Nottingham Forest.
"Out of everything, I have probably missed the fans the most. I love playing at the City Ground.
"I know people talk about Barcelona, this game and that game, but I just love matchdays at the City Ground."
Source: PA
Source: PA