The news was first reported by WoW Insider.
"An opportunity has come my way, and I have made the very tough decision to move on from Blizzard," said Street, who joined the studio in February 2008.
Street had been one of the most prominent public-facing figures on the World of Warcraft development team, fostering a direct line from players to Blizzard developers through regular interactions on the game's forums as well as on his personal Twitter account, which currently has more than 70,000 followers. As lead systems designer, he and his team were responsible for building and changing the fundamentals of the way World of Warcraft plays, including classes, game mechanics, items, trade skills and user interface.
"I wanted to thank all of you for being a part of this grand quest," Street continued. "I have said a hundred times that having passionate gamers, including the angry ones, is a far better place to be than having a community that doesn't care. You all care. Like us, you want the game to be the best that it can be. So I ask you to keep on providing your feedback. I promise (and I rarely promise!) that the developers care very much about what you have to say."
Update: Reached for comment, a Blizzard representative told Polygon, "We had a great time working with [Street] and appreciate all his contributions on World of Warcraft, and we wish him all the best."