Kei Watanabe is a multifaceted Japanese entertainer, recognized for his work as an actor, scriptwriter, and director, with a portfolio that also includes voice acting in anime. He was born on June 16, 1976, in Osaka Prefecture, Japan. His career in the entertainment industry began in the early 1990s, initially gaining attention as an on-screen actor. He appeared in numerous television dramas throughout the 1990s, with some of his notable early roles including the Fuji TV series Doku in 1996 and the TBS drama Risukî gêmu, also in 1996. His work as an actor earned him the Golden Arrow Award for New Comer in 1994.

In the mid-2000s, Watanabe expanded his creative repertoire to include voice acting for anime. One of his roles from this period is Ken Ryuushou in the 2006 television anime series Jinzo Konchu Kabuto Borg VxV. The series, which aired from October 2006 to October 2007, follows enthusiasts of Battles with beetle-like machines known as KabutoBorgs, with Watanabe providing the voice for Ken, a friend of the main protagonist. During the same era, he voiced other anime characters, including Katsuo Mizuno in the long-running series The Prince of Tennis, Shinagawa in Dr. Rin ni Kiitemite!, and Flames Bomber in Bomberman Jetters. His voice acting credits also include a role in the popular series Ouran High School Host Club, where he voiced Yasuchika Haninozuka.

While his voice acting work is a notable part of his career, Watanabe's primary professional focus shifted significantly towards writing. He began writing scripts in the early 2000s and won the Japan TV Scenario Touryuumon prize in. Subsequently, he concentrated on scriptwriting, becoming the primary writer for many television drama series. His extensive writing credits include numerous episodes for popular dramas such as Tumbling, Rescue: Tokubetsu Koudo Kyuujotai, and several installments of the High & Low franchise. In 2006, he formed a writers' unit named AOI with Takamichi Yamada, through which they have worked on manga and stage play scripts and direction. His work as a scriptwriter and director has continued into the 2020s, with recent credits including the 2023 TBS Sunday drama Get Ready! and the 2026 TBS network drama Tagusari Brothers. Throughout his career, Kei Watanabe has been managed by the talent agency LDH.