The world number four made the announcement on the eve of the WGC-Bridgestone Invitational in Ohio, bringing an end to Fitzgerald's nine years of service.
Close friend Harry Diamond will now take over bag duties as McIlroy aims to pick up a first victory of 2017, while his hunt for a Major stretches to three years following his recent disappointment at The Open.
"It's a big change," he told reporters. "JP has been a huge part of my life for the last decade. We started in July 2008 and went all the way up until July of this year. A lot of great times; a lot of great times on and off the golf course. I still consider JP one of my best friends, one of my closest friends, but sometimes to preserve a personal relationship you might have to sacrifice a professional one and that was sort of the decision that I came to in the end.
"I was getting very hard on him on the golf course and I didn't want to treat someone like that. I thanked JP for everything. JP knows how much I think of him, how much he means to me, what we've achieved together, and it wasn't an easy decision. But I felt like it was a change that I needed to make because I got to the point where, if I didn't play a good shot or if I made a wrong decision, I was getting more frustrated at him than I was at myself.
"I would much rather be angry at myself for making a wrong decision than being angry at him. There's nothing to say that JP mightn't work for me again at some point but right now I just felt like I needed a little bit of a change. I just changed my path a little bit, but maybe in the future that path might come back to where it was. Right now I just needed to mix things up a little bit. JP understood that and we're still all good."
McIlroy won four Major titles during his time working with Fitzgerald, as well as spending a cumulative total of 95 weeks as world number one.