Katsuhito Ishii was born on December 31, 1966 in Niigata Prefecture, Japan. He graduated from the Department of Visual Communication Design at Musashino Art University, where he studied under the influence of director Kohei Oguri. After joining the production company Tohokushinsha Film in 1991, Ishii began directing television commercials in 1992, an area in which he would go on to win several awards. His first short film, The Promise of August, was released in 1995 and won a grand prize at the Yubari International Fantastic Film Festival.

Ishii made his feature film directorial debut with Shark Skin Man and Peach Hip Girl in 1998, an adaptation of the cult manga by Minetaro Mochizuki. He followed this with Party 7 in 2000, another manga adaptation that displayed a shift toward a more eccentric and stylized form of black comedy. While he has directed several live-action films that have been recognized at international festivals, including The Taste of Tea which opened the Director's Fortnight at the Cannes Film Festival, Ishii is also a significant creator within the animation industry.

His work in animation is defined by original creations rather than adaptations. In the early 2000s, he created the 3D animated short Hal & Bons and the 2D space opera series Trava: Fist Planet, where he served as director. He further contributed to Quentin Tarantino's Kill Bill: Volume 1 as a character designer and storyboard artist for its animated sequence. Ishii is most widely recognized for his role as the original creator of the 2010 film Redline. For this project, he is credited as the original story writer, screenwriter, and character designer. The film, produced by Madhouse, took seven years to complete and stands as a landmark of hand-drawn animation. He has also served as the original concept writer and screenwriter for the Gambo segment of the anthology film Short Peace.

Ishii established his own production company, Nice Rainbow, in October 2006. His artistic identity is heavily graphic and stylized, reflecting his background in commercial direction and a deep affinity for manga and storyboarding. Academic analysis of his work, particularly The Taste of Tea, suggests that his narratives often use the monstrous or the fantastic as a method to interpret and mediate contemporary cultural anxieties. This approach creates a distinct blend of surreal humor, pop aesthetics, and deadpan emotional weight that carries across his live-action and animated projects. He has also worked as a creative advisor on the Lupin the Third spinoff films. Through works like Redline, Ishii has established himself as a significant industry figure who bridges the worlds of independent live-action cinema and high-budget, auteur-driven anime.