He is Ireland’s most capped player and was granted an early release from his contract, which had been set to expire in June 2016.
Donnacha, previously representing Cork Consitution, Highfield and CB had capped 268 victories for Munster.
The 36 year old joins Worcester for two year contract.
As a Munster player Donnacha O’ Callaghan won two European Cups in 2006 and 2008, three Pro12 and a Celtic Cup.
A statement from O’ Callaghan states:
“It has been a huge decision for me to leave Munster, one that I have thought long and hard about. 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.”