The 17-year-old midfielder made his first-team debut as a substitute against Burnley last September.
Boss Lee Clark's faith in him has been underlined by three further appearances this month, including a start in the FA Cup win over Bristol Rovers.
Brown has been with City since the age of 10 and has represented England at Under-16 and Under-17 levels.
Birmingham City prospect Reece Brown has signed a two-and-a-half-year professional contract with the club.