The 29-year old has agreed a switch to the Aviva Premiership side after six years at the Liberty Stadium.
Walker joined the Ospreys from Borders in the summer of 2006 since when he has made 103 appearances for the region, bringing his century up against Newport Gwent Dragons in April last year, and has scored 37 tries. He has yet to feature this season for the Ospreys after suffering an ACL injury on international duty last August, ruling him out of the Rugby World Cup, but is nearing a return to full fitness.
Speaking about his decision to move to Worcester, Walker commented:
"My six years at the Ospreys have been the best of my career and I'm sad to be moving on, but after 10 years playing in the Celtic League I feel that the time is right for me to try a fresh challenge in England.
"Everybody at the Ospreys have always been fantastic to me, particularly over the last year while I've been injured. The medical team, coaches and management have been great, while the fans have always given me their full support.
"I'll leave the Ospreys with so many happy memories, and I'd like to thank everybody for always making me feel at home during my time with the region."
During his time with the Ospreys, Walker has won two Celtic League titles as well as appearing at consecutive EDF Energy Cup Finals against Leicester Tigers at Twickenham, and featuring in the historic win over Australia.
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