The 24 year old signs on a deal reportedly worth £1 million at it's fruition has only played 28 games as a professional but has scored 12 goals in League One, he signed a three and a half year deal for Steve Bruce's side.
Campbell's rise to prominence came last year for Yeading however after starting with Chesham in 2001 the five year rise to the top has been amazing.
The move has been a suprise to all staff and supporters at Brentford who have only been in contact with Birmingham since lunchtime and no one from the club has commented.