Leicester, Watford and Burnley were also chasing his signature.
Manager George Burley said: "It has been pending for a while but I am delighted everything is sorted.
"He is a smashing player who showed his qualities at the end of last season and I am very pleased to have him on board for the new campaign."
Saganowski's scoring streak also saw him reclaim his place in the Polish international squad at the end of the campaign.