The Barclays Premier League club confirmed the switch in a statement on their website.
Bentley joined Spurs from Blackburn in 2008 for £15million having started his professional career at their north London rivals Arsenal.
The 28-year-old has found first-team action at White Hart Lane hard to come by, though, and has spent time out on loan at Birmingham and West Ham.
Bentley, who has won seven caps for England, underwent surgery after suffering a serious knee injury while at West Ham last October.
- Barclays Premier League