The former All Black has played 94 competitive matches for the two-time Heineken Cup champions since making his debut against ASM Clermont Auvergne in January 2008 and is the current squad's leading try scorer with 32.
He takes over from O'Connell who has been squad captain since 2006/2007. O'Connell said: " I've been squad captain for six seasons and just felt it was time to step back and let someone else assume the role. I thought the timing was right with the new coaching structure and I think we're unbelievably fortunate to have a player of Doug's calibre to step in. He brings a wealth of experience and an exemplary work ethic to the job that can only benefit Munster Rugby in the season ahead."
Head Coach Rob Penney said: "The process to select a new captain has been on-going for the past number of weeks and involved discussion with players and staff. It's never easy to replace a player of Paul O'Connell's stature but then again, as Paul said, we are indeed fortunate to be able to turn to Doug to take over the role. I'm just delighted to have him as squad captain. I know he'll do a first rate job."
Howlett said: "I think it's such a great honour to have been asked to captain this squad. It truly is one of the highlights of my career. I know I've got big boots to fill following Paul, Axel [Anthony Foley], Mick Galwey and Jim Williams. And I'm also aware of the number of leaders in this squad, people well capable of doing this job and that makes my appointment all the more worthy and humbling."