Broadhurst replaces Paul Merson, who was sacked as playr-manager ahead of the game with Scunthorpe.
He said: “My initial task is to guide the club to League One safety and supporters can be assured I’ll be totally focused and work very hard to achieve that objective.
“I have got a great deal of experience to fall back on and I’m looking forward to the challenge as long as I have the full support of my coaching staff, players and just as importantly, our supporters.”
Broadhurst played 147 times for Birmingham in the 70s and 80s, and had a spell on loan with the Saddlers.
He has been assistant manager at Blues, and also boasts managerial experience at Northampton Town.