The actors will join already-announced Peter Cullen and Frank Welker to voice characters in the fourth offering of the movie franchise.
Goodman will play Autobot Hound, Watanabe will play Drift and Welker will play Galvatron, joining Cullen, who reprises his role as Optimus Prime.
"I am pleased to welcome two gifted and versatile actors, John Goodman and Ken Watanabe, to the world of Transformers," Bay said in a release. "And to reteam with Peter and Frank, who have brought Transformers characters alive from the beginning. I've been fortunate to work with some of the best voice talent in the business, and together we will introduce several exciting new robots to fans of the franchise around the world."