"This is a fantastic piece of business for us at a really good price," Latics boss Owen Coyle told the club's official website.
"Grant is a proven goalscorer at every level and he will definitely bring something new to the table that we were missing in the squad.
"There is already a great buzz about the place since the new boys have started coming through the door and this is another one that will really lift the place.
"He's been a hero to the fans at every club he's been and I know the Norwich fans are sad to see him go, he's been one of the icons of their success in recent years. But now it's the Wigan fans' turn to enjoy him and we're all delighted he's coming on board."