The right winger signed for Spurs from Blackburn in 2008 for £15million and was rated at the time as one of England's hottest prospects.
But the 26-year-old has endured a tough time at White Hart Lane and been pushed further down the pecking order, behind Aaron Lennon.
Loan spell: The 26-year-old, who has won seven England caps, will spend six months at Birmingham
He played just over 40 games for Spurs, though Redknapp believes that the spell with Birmingham will do the midfielder good.
Bentley has won seven caps for England, but the last one came in a friendly against Switzerland in February 2008.
More will follow.
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Explore more:People: David Bentley, Aaron Lennon Places: Birmingham, United Kingdom, Switzerland