Mitch Hancox has put pen-to-paper on a three-year contract with Blues.
The 19-year-old left-back's new deal will run until the end of June 2016.
Hancox, who is a product of the club's Academy, made his first team bow for the club in October 2012 as a late substitute against Huddersfield Town. He later went on to make 20 appearances for Lee Clark's side during the 2012/13 campaign.
He missed the final game of the npower Championship season after breaking his hand, but is expected to be fully recovered in time for pre-season training in late June.