Kenji Sahara was born Tadashi Ishihara on May 14, 1932 in Kawasaki City, Kanagawa, Japan. He came in second in the "Mr. Ordinary Contest" in 1953 and his cinema debut was as an extra in two small roles in Gojira (1954), one as a ship passenger and one as a journalist. However, his break-through in Toho Studios' sci-fi films came when he portrayed the male lead Shigeru in Sora no daikaijû Radon (1956), where he changed his name to "Kenji Sahara." He would go on to become a familiar face in Toho's sci-fi films, playing a wide variety of heroes and villains. Appearing in films from all three of the Godzilla series, "Showa, "Heisei," and "Millennium," Sahara has appeared in Godzilla films more than any other actor. He is also a regular cast member in Japan's "Ultraman" television shows.

With his wife, who is fluent in English, they have visited the United States several times.