Ken Watanabe began his career on stage, with the Tokyo-based theater troupe Madoka. While working with Madoka, he was selected to portray the hero role in the play "Shimodani Mannen-cho Monogatari", directed by Yukio Ninagawa. His performance attracted critical and popular notice.

In 1982, Watanabe made his television debut in "Michinaru Hanran" (Unknown Rebellion). In 1987, he displayed a regal bearing and powerful presence in NHK’s successful Samurai drama series, "Dokuganryu Masamune", and went on to earn acclaim in such historical dramas as the TV shows "Oda Nobunaga", "Chushingura", and the movie Bakumatsu Junjyo Den.

Additionally, Watanabe’s consummate skills have contributed to such projects as Ikebukuro West Gate Park, Anata ga Hoshii (I Want You) for television and the movies Space Travelers, Oboreru Sakana (Drowning Fish) and The Sun Rises Again.