The 18-year-old has been with Blues on a non-contract basis since last summer, after being released by Everton where he was a trainee.
Higgins, who hails from Liverpool, is predominantly a right back, but he can also play in midfield.
He has been a regular in Richard Beale's development squad, where he has put in a number of assured performances.
Lee Clark's decision to give him a squad number has come about because of a host of injuries to senior players.
Higgins, who gets the number 40 shirt, joins the likes of Marcel Henry-Francis (another non-contract player), Eddy Gnahore, Nick Townsend, James Fry, Reece Hales, Josh Hawker and Emmitt Delfouneso in being promoted to the first team squad in recent weeks.