Kenji Kamiyama was born on March 20, 1966, in Saitama Prefecture, Japan. His entry into the animation industry was unconventional, beginning with background art. He joined Studio Fuga in 1985, where he worked on background production for major films such as Akira and Kiki's Delivery Service. After a period as a freelancer, he joined Production I.G in 1996, where he came under the tutelage of renowned director Mamoru Oshii. Kamiyama worked in various capacities on Oshii-led projects, including as a unit director on Jin-Roh: The Wolf Brigade, before writing the screenplay for the acclaimed short film Blood: The Last Vampire in 2000. He made his directorial debut in 2002 with the comedic short series MiniPato.

Kamiyama gained international recognition as the director and chief writer of the television series Ghost in the Shell: Stand Alone Complex and its sequel, 2nd GIG. Rather than directly adapting Masamune Shirow's original manga, he constructed a new parallel narrative set in a different timeline, exploring themes of cyberterrorism, social alienation, and political corruption. The success of this series cemented his reputation as a major directorial talent within the industry.

As an original creator, Kamiyama is best known for conceiving and writing the 2009 television series Eden of the East. The story, which follows a young amnesiac who becomes entangled in a deadly game to save Japan, was entirely his own creation. He continued this original narrative across two feature films, Eden of the East: The King of Eden and Eden of the East: Paradise Lost, as well as the compilation film Eden of the East: Air Communication. His other major original film is Napping Princess (2017), which he both wrote and directed. Set in Japan on the eve of the 2020 Tokyo Olympics, the story blends a young girl's reality with a dreamlike fantasy world of giant robots and magic. He is also the creator of the short film Xi AVANT.

Beyond his original works, Kamiyama has a significant history of adapting existing properties. In addition to his work on the Ghost in the Shell franchise, he has directed the television adaptation of the fantasy novel series Moribito: Guardian of the Spirit, the CG-animated feature 009 Re:Cyborg based on the classic manga Cyborg 009, and the CG series Ultraman. He has also ventured into international franchises, co-directing Blade Runner: Black Lotus and directing an episode of Star Wars: Visions, as well as The Lord of the Rings: The War of the Rohirrim.

Several recurring thematic preoccupations define Kamiyama's artistic identity. A frequent subject is the nature of memory, amnesia, and identity, which serves as a core plot device in both Ghost in the Shell: Stand Alone Complex and Eden of the East. His work is also characterized by a critical examination of Japanese society, including the political establishment and the social consequences of terrorism, reflecting what sources describe as a broadly anti-authoritarian perspective. He frequently explores the power and danger of information networks, often using complex, multi-layered plots that require active engagement from the viewer.

Kamiyama is considered a significant figure in modern anime, particularly for his role in the late 2000s as a creator of intelligent, mature-oriented television science fiction. His career path is notable for the rare transition from background artist to internationally acclaimed director and writer. After working extensively with Production I.G, he founded his own company, STEVE N'STEVEN, in 2011 to focus more on 3D CG animation production. While highly respected for his narrative depth and direction, some analyses note that his work is often more popular with international audiences than domestically in Japan.