The 28-year-old came off the bench during the Blues' 3-0 win over Leeds United in the third round of the FA Cup.
He has signed a contract which is expected to run up to the end of the 2007/8 season.
The 1.25 million pound transfer from Burnley ends weeks of speculation surrounding his future.
Nottingham Forest failed to lure Blake in a two-player swap deal while Wigan Athletic offered #700,000 for the player who left Valley Parade almost three years ago.