The announcement was made Thursday, two-plus months before Detroit-based Quicken Loans brings a PGA Tour event to the Motor City for the first time.
Johnson is currently the No. 1 player in the world ranking, Fowler is No. 10, and Watson ranks No. 17.
Kevin Kisner, Charles Howell III, Si Woo Kim, rookie Cameron Champ, Billy Horschel, Aaron Wise, Jason Dufner and Lucas Glover have also committed to play in Detroit. The competition June 27-30 at Detroit Golf Club will be two weeks after the U.S. Open and four weeks before The Open, giving organizers hope that more stars will join the field.