Roche, who announced the decision on his 33rd birthday, joined Irish from Saracens in January 2003 and has made 179 appearances for the Exiles to date.
He won the club's player of the year award in 2005/2006 and has appeared in both the second and back row for Irish and represented England at Sevens, U19, U21, and A levels.
Head coach Toby Booth said: "Kieran has been one of London Irish's greatest servants. A true professional and we thank him for his outstanding dedication and commitment to the club.
"We would like to wish him and his family all the very best for the future. We know that he will be successful in his future career and we wish him luck."
Roche said: "I would like to thank everyone who has played a part in my rugby career, from my school days onwards, including the players, coaches and support staff that I have worked alongside both at Saracens and London Irish.
"I would also like to thank the supporters of both clubs; particularly those at London Irish who have made me feel a real part of such a great club for the last 10 years."
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