Birth place: Tokyo, Japan.

After graduating from high school, Dezaki took a position at Toshiba while studying in the department of literature at Hosei University. While doing both of these, he continued to work on his dream job of working on movie production. He acted as the coach for the nine-member volleyball team at Toshiba. Dezaki also began pulling together an anime production team.

Dezaki resigned after working for seven years at Toshiba, leaving Hosei University in the middle of a term as well. He began working for Gisaburou Sugii's company Art Fresh, working alongside his younger brother Osamu. His first works included writing the script for Attack No.1 and storyboarding Kyojin no Hoshi.

In 1969, Dezaki became a freelancer, doing scripting, production and direction work for Tokyo Movie Shinsha, Tatsunoko Production, and Sunrise. In 1977, he founded Magic Bus and produced and animated Shin Kyojin no Hoshi.

His younger brother is the anime director Dezaki Osamu.