The Captain has committed his future until June 2023.
Dean's previous contract was due to end this summer.
Securing Dean is another step in the process of planning for the here and now and the future with a core group of key players.
Dean, 28, has been a hit since his move from Brentford in August 2017.
The centre-half is closing in on a century of appearance for Blues.
He is an important influence on and off the pitch and Head Coach Pep Clotet named him Captain last week, to lead Blues into 2019/20.
This summer Blues have bolstered the ranks with the signings of Gary Gardner, Dan Crowley, Jake Clarke-Salter, Ivan Sunjic, Agustin Medina and Ivan Guzman.
Dean follows Lukas Jutkiewicz and Connal Trueman in signing new contracts, whilst young talents of the like of Steve Seddon, Odin Bailey, Geraldo Bajarami, Zach Jeacoack and Jude Bellingham have also been engaged this summer.