At that stage, the 34-year-old former All Black was in contract extension negotiations with Munster but has not been able to play since because of the shoulder injury he suffered in the course of scoring Munster's third try.
He underwent surgery in a Dublin hospital earlier this month and acting on medical advice will retire at the end of the season.
Howlett joined Munster in January 2008 and played a key role in their Heineken Cup success that season.
He won his 100th cap against Leinster in the October 2012 league derby and ends his Munster career as their second leading try scorer of all-time with 35 tries after five and-a-half seasons.
He became just the second overseas player and the first back to be nominated squad captain at the start of the current season.
Howlett has intimated that he will remain on in Cork for the immediate future where he lives with his wife and three children.
Other departing players from the current Munster squad - besides Peter Stringer who remains with Bath, Marcus Horan, who announced his retirement recently, Sean Scanlon (Rotherham Titans) and Sean Henry (Connacht) - include Wian du Preez who returns to his native South Africa, Scott Deasy and Christy Condon.
BJ Botha will continue on with Munster having signed a two-year contract extension, while Danny Barnes has not been re-contracted but is understood to have negotiated an opportunity to play abroad and news of that will be confirmed in the coming weeks.