The 23-year-old has penned a three-and-a-half year deal, keeping him at Dean Court until summer 2016.
The Cherries have been chasing Ritchie for a while, putting in a bid in December 2011 which was rejected.
Ritchie, who has scored 10 goals this season, should go straight into this weekend's squad to face MK Dons.
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Pitchside Europe - Mon, May 20, 2013 12:38 BST