He was born in Soma City, Fukushima Prefecture (some sources say Tokyo,
where he graduated). He is brother of also animation director Osamu
Dezaki. In the 60s he joined his brother in an animation studio, but as
a writer. Later he becomes free-lance writer until 1977, when he
co-founded Magic Bus animation studio. Here he begins to direct his own
scripts and adaptations. His debut as a film director was "Captain"
(1981), based on the manga by Akio Chiba. In 2000 he was awarded by the
Ministry of Health and Welfare.
His younger brother is the anime pioneer Osamu Dezaki.
After graduating from high school, Dezaki took a course in the department of literature at Hosei University.
While at Hosei University, Dezaki took a job at the Toshiba corporation for a period of seven years; during that time he acted as the coach for the company's nine-member volleyball team.
In 1977, he founded the Magic Bus studio, an animation production company.