Arguably one of the greatest players of all-time, the legendary All Black is to return home to New Zealand in August to take up business interests, after tying up some loose ends in Ireland.
Unfortunately dogged by injuries for the majority of his time with Munster, Cullen is honest enough to admit that his body has taken enough punishment.
He said: "I've hung up the boots for good. My mind is fresh and feels like I could sign another four-year deal and keep going but there comes a time when you have to be a realist and I know my body has had enough.
"I can't remember the last time my ankles and knees didn't ache. And at the back of my mind I'm always worried that I might be a tackle away from injuring the shoulder again.
"So, in the end, it's an easy decision to retire. I will miss a lot of things about the game but I can't sign a new deal knowing my body has had it."
The Paraparaumu-born player still holds the Test try-scoring record for the All Blacks, with 46 tries in 58 matches for New Zealand. Cullen made a total of 44 appearances for Munster, having signed for the province in 2003.
His best season for Munster came in 2003/04 when he touched down eight times in 15 games in the Celtic League. He scored his 14th and last try for Munster against Connacht in the Magners League in December.
"I have loved every minute of my time in Ireland - apart from the injuries," Cullen added.
"The club and supporters have been terrific to me but I can't help feeling that I have let them down. When I signed in 2003 I felt like I could reproduce the type of performances I was able to put on for the All Blacks.
"But three shoulder operations put paid to that. Munster will always hold a special place within me. The toughest thing about retiring is walking away from Thomond Park. I just wish I could have done more for the club, my team-mates and Munster's great supporters."