Davies makes cross-city switch to Birmingham
Manager Gerard Houllier said: "We have four centre backs in James Collins, Richard Dunne, Carlos Cuellar and Ciaran Clark. Curtis was not getting enough time to play and I understand that.
"He goes with our best wishes and I hope this move will help in his career development because he is a nice lad."
Davies looked set for a terrific second full season at Villa in 2009-10 campaign after starting the campaign as a central defender alongside Carlos Cuellar.
He even managed to bag a crucial second goal in the 3-1 win at Anfield against Liverpool but a shoulder injury to correct a long-standing problem put the classy stopper's season on hold.
Surgery was required and, unfortunately for Davies, when he returned to full fitness Villa were in the throes of a terrific defensive run.
He did make the bench for the remaining months of the season and even managed a run-out as a substitute in the 3-2 home win over Brighton in the fourth round of the FA Cup but ultimately his season was frustrating.
Having endured a somewhat disappointing campaign during his time on loan from West Bromwich Albion, Davies enjoyed a much better second season once he had officially completed his move from The Hawthorns and become a full-fledged Villan.
He played in most matches, regularly producing the classy form which had persuaded the club to sign him.
He also scored his second goal in claret and blue - ironically against the Baggies.
And where he had been unable to suppress his delight when he opened his account at Wigan in December 2009, he was subdued on this occasion, not wishing to insult his former club.
Davies, who began his career with Luton Town, became Albion's most expensive defender when he joined them for £3m in 2005.
The 25-year-old central defender joined Villa on a season-long loan from the Baggies in August 2007 before the move was made permanent.
Davies made 66 appearances for Villa and scored three goals.