كتب : Hatem Maher
"We are very happy that we could persuade Mikael to join Hannover," sporting director Christian Hochstatter told the club's website.
The 27-year-old has signed a deal that will keep him at Hannover until the summer of 2011.
Forssell scored nine goals with Birmingham last season but his efforts were to no avail as the team were relegated to the Championship.