Yoh Yoshinari was born in Tokyo on May 6, 1971. He graduated from Tokyo Designer Gakuin College and entered the anime industry through the influence of his older brother, Kou Yoshinari, for whom he worked as an uncredited assistant during high school. After professional school, he briefly joined Madhouse before moving to the studio Gainax, where he worked for many years. In 2011, he was among the former Gainax employees who left to help found Studio Trigger.

As an original creator, Yoshinari is best known as the concept creator, director, character designer, and animation director behind the Little Witch Academia franchise. The first Little Witch Academia short film was produced in 2013 as part of the Young Animator Training Project, a Japanese government-funded initiative in which young artists collaborate with established studios. Yoshinari served as director, character designer, and animation director on this short, taking on a mentorship role for the younger staff members. Due to the success of the original short, a sequel film titled Little Witch Academia: The Enchanted Parade was funded through a Kickstarter campaign that raised over $625,000, far exceeding its original goal. Yoshinari directed this film as well. The franchise later expanded into a full television series in 2017, with Yoshinari again serving as director, marking his first time directing a full-length series. A manga adaptation, Little Witch Academia: Tsukiyo no Ōkan, is also part of this expanded universe. Beyond the world of Little Witch Academia, Yoshinari is also the director of the original television series BNA: Brand New Animal, which was announced by Studio Trigger in 2019.

While he is an acclaimed original creator, Yoshinari's career is deeply rooted in key animation, storyboarding, and character design for a wide range of major anime productions. His filmography includes work on landmark series such as Neon Genesis Evangelion and its film The End of Evangelion, as well as FLCL, Gurren Lagann, Kill la Kill, and Promare. He also served as character designer for the Netflix series Cyberpunk: Edgerunners. Yoshinari's work on the Valkyrie Profile video game series, for which he provided concept art and character designs, is also notable.

Yoshinari is recognized for a distinct animation style that emphasizes volume and perspective, particularly when depicting effects like smoke and explosions. His key animation is often described as dense and dynamic, with a strong sense of movement and composition. Hiroyuki Imaishi, a frequent collaborator, has described Yoshinari's style as a bundle that takes the best elements from various legendary animators. In interviews, Yoshinari has cited the Japanese work Nijitte Monogatari as a major influence, and counts American creators such as Genndy Tartakovsky, Craig McCracken, and Lauren Faust among his favorites.

Yoshinari's significance in the industry stems from his dual role as a master animator and a visionary director. He is a key creative pillar of Studio Trigger, and his work on the Little Witch Academia franchise is a prime example of an original property that grew from a small-scale, government-supported project into a successful international multimedia franchise. His creative choices often reflect a desire to explore traditional Western themes, such as magic schools in Little Witch Academia or the idea of a refuge for different beings in BNA: Brand New Animal, through a distinctly Japanese lens.