The Finland international, who is on a season long loan deal at St. Andrews from Chelsea, earned the award for netting six goals in five games for Steve Bruce's side last month.
Forssell currently has 18 league and cup goals to his name so far this season - 16 of those coming in Premiership games.
"Forssell has been in superb form on loan from Chelsea for the Blues this season and it is no surprise that Birmingham are looking to sign the striker permanently," Nic Gault, of the Barclaycard Awards Panel, said.
"I am sure every City fan and all connected to the club will be very pleased that he has received this award."
Chelsea manager Claudio Ranieri was named the Barclaycard Premiership manager of the month for March.