Osamu Dezaki was born in Shinagawa, Tokyo on November 18, 1943. He debuted as a manga artist while he was still in high school. In 1963, Dezaki joined Mushi Productions, the anime studio founded by Osamu Tezuka. In 1972, Dezaki co-founded the anime studio MADHOUSE. Later, Dezaki and Akio Sugino would co-found Studio Annapuru.

Dezaki made his directorial debut in 1970, when he directed the Tomorrow's Joe anime series; he also directed the Tomorrow's Joe movies and the second television anime series. His credits for directing also include Ace wo Neare! (the movie, television series, and the OAV), the film Air, the first two Astro Boy series, the B.B OAV, Big X, Black Jack (the OAV and the movie), the Clannad film, Dororo, Ganba no Boken, Genji Monogatari Sennenki, the Gense Shugoshin P-hyoro Ikka OAV, Golgo 13 (the Queen Bee OAV and The Professional film), Hajime Ningen Gyatoruz, Hakugei: Legend of the Moby Dick, the Ie Naki Ko movie, In the Beginning - The Bible Stories, Jetter Mars, Jungle Kurobe, Karate Baka Ichidai, the Kasei Yakyoku OAV, several Lupin III television specials, Manga Sekai Mukashi Banashi, Nobody's Boy - Remi, Oniisama E..., The Rose of Versailles, The Snow Queen, Space Adventure Cobra (the television series and the film), the Sword for Truth film, Takarajima, the film A Time Slip of 10000 Years: Prime Rose, two Hamtaro films, Ultraviolet: Code 044, and the film Undersea Super Train: Marine Express.

Dezaki also did storyboard work on Akado Suzunosuke, supervision on the Botchan special, screenplay and storyboard for Cobra the Animation, key animation for the Kanashimi no Belladonna film, storyboards for the Samurai Giants anime series, art for the Senya Ichiya Monogatari film, and served as the executive director for the Sohryuden - Legend of the Dragon Kings OAV.

Dezaki also did some anime work under the name of Makura Saki. He used this name on such projects as Ace wo Nerae!, Andersen Stories, Tomorrow's Joe 2, Hazedon, Karate Baka Ichidai, three of the Lupin III television specials, New Moomin, One Pound Gospel, The Rose of Versailles, and Space Adventure Cobra. The credits under this pseudonym include storyboarding, episode directing, directing, and continuity.

In addition to his anime work, Dezaki did animation work for the Rainbow Brite series, and he also served as the animation director for The Visionaries and as a director for Bionic Six and Mighty Orbots.

Sadly, Osamu Dezaki passed away on April 17, 2011 at the age of 67 due to lung cancer. He is survived by his brother, Satoshi Dezaki, who is also a director.