In his time with the province he was won two Heineken Cups, in 2006 and 2008, three PRO12 titles, in 2003, 2009 and 2011, and a Celtic Cup in 2005.
Last year the lock made 17 appearances in the GUINNESS PRO12 and Foley admits Munster's most capped and senior player will be sorely missed.
"I had the honour of playing with Donncha for over a decade and have witnessed first-hand everything he has achieved with Munster and Ireland," he said.
"A true Munster man in every sense, his passion and commitment were clear for all to see. He is held in the highest regard on the world stage after excelling at every level and we are thankful for his immense contribution to the province."
The 36-year-old commenced the 2015/16 season by featuring in all three of Munster's pre-season games with his last appearance taking place on home soil in Cork last Friday night against London Irish where he was supported by his wife Jenny and family.
Fittingly the Cork-native made his Munster debut at the same venue when lining up against Edinburgh Reivers in August 1998 at 19 years of age. Two months later he made his European debut against Perpignan at Stade Aime Giral.
On the International front O'Callaghan has made 94 appearances for his country.
"It has been a huge decision for me to leave Munster, one that I have thought long and hard about," he said.
"The opportunity to prolong my career is one that I couldn't pass up and I'm extremely grateful to Munster, the IRFU and Worcester for providing me with this opportunity.
"Playing for both my home province and country has been a dream come true for me and my family, I have loved every moment of it. I leave with a full heart and unbelievable memories.
"I'm forever grateful to those in Munster and Irish Rugby that put the structures in place all the way up, and most importantly, the people that have influenced and shaped me not only as a player but as a person.
"My goal is the same now as it was when I was eight years of age, to play rugby, enjoy it and win. I look forward to earning the respect of the Worcester management, players and supporters.
"Finally I would like to thank the Munster supporters - for over 17 years you have lifted me to play beyond myself and I look forward to going back and joining you in my first role with Munster, as a supporter."
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