Trained, as a youth, in a Christian seminary for the priesthood in Japan. However, while he was there, something happened (which he refuses to discuss publicly) that shattered his religious leanings. He remains fascinated by Christianity, however, and often alludes to the Bible in his films. There is some debate among his fans about whether Angel's Egg (1985) is an allegory for his loss of faith.
One of the co-founders of Studio Ghibli along with Hayao Miyazaki and Isao Takahata but left over creative differences. Despite their differences, Toshio Suzuki and Studio Ghibli would later help Oshii with his production of Kôkaku kidôtai: Stand Alone Complex (2002).Oshii maintains skeptical, but respectful, views of each of Takahata and Miyazaki's films; he has been critical of Miyazaki's attitude towards his workers, but also claims that he would feel "strangely empty" and "it would be boring" if both Miyazaki and Takahata stopped making films.
Oshii has stated his approach to directing is regarding the visuals as the most important aspect, followed by the story and the characters afterwards.
He has worked on three animes: Urusei Yatsura, Patlabor and Ghost in the Shell; the former was an outright comedy and the latter two were drama shows but were fairly comedic. Oshii adapted these into films; he strayed from the source material by removing their comedy and giving them a darker atmosphere, which was a point of controversy for some fans ("Urusei Yatsura" creator Rumiko Takahashi was particularly upset with what he'd done with her story).
According to Oshii, "Kenji Kawai's music is responsible for 50 percent of [his] films' successes" and he "can't do anything without [Kenji Kawai].".