Casey Hudson has left BioWare to "take a much needed break" before pursuing "a new set of challenges".
He leaves the firm after almost 16 years, most recently overseeing the Mass Effect series in the role of executive producer. He was believed to be working on both the next Mass Effect and a new IP.
"After what already feels like a lifetime of extraordinary experiences, I have decided to hit the reset button and move on from BioWare," Casey wrote in a message to colleagues on the BioWare Blog. "I'll take a much needed break, get perspective on what I really want to do with the next phase of my life, and eventually, take on a new set of challenges.
"Though there's never an easy time to make a change like this, I believe this is the best time for it. The foundation of our new IP in Edmonton is complete, and the team is ready to move forward into pre-production on a title that I think will redefine interactive entertainment. Development for the next Mass Effect game is well underway, with stunning assets and playable builds that prove the team is ready to deliver the best Mass Effect experience to date. And the Dragon Age: Inquisition team is putting the final touches on a truly ambitious title with some of the most beautiful visuals I've seen in a game.
"But while I feel that the time has come, this is without a doubt the most difficult decision of my career. BioWare is as magical a place today as it was when I started. The projects we are working on are some of the most exciting and prestigious in the world. The talent in our teams is second to none. And the people here are some of my closest friends. I've spent more time with many of you than my own family, and I have enjoyed every day of it."
BioWare adds that it will "continue working on the next Mass Effect game and our new IP project, confident in our goals and progress".
BioWare's latest title - rumoured to be called Shadow Realms - is expected to be revealed during Gamescom next week.
VideoGamer.com has contacted EA for further comment.