The Monuments Men star Goodman will provide the voice of Hound, while Watanabe has joined the all-star cast as Drift.
They join Peter Cullen (Optimus Prime) and Frank Welker (Galvatron) among the voice stars of the new blockbuster, which is currently in post-production.
Mark Wahlberg, Nicola Peltz, Stanley Tucci, Kelsey Grammer and Sophia Myles are among the human stars of the movie.
Announcing the latest casting news in a statement released on Thursday (08May14), director Bay says, "I am pleased to welcome two gifted and versatile actors, John Goodman and Ken Watanabe, to the world of Transformers. And to re-team 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."
Transformers: Age of Extinction, the fourth installment in the franchise, will be released in cinemas at the end of June (14).