Isayama was born on August 29, 1986 in Ōyama, Ōita, Japan. After graduating Ōita Prefectural Hitarinkou High School, he matriculated in the cartoon design program of the cartoon arts department, Kyushu Designer Gakuin. After graduating, he moved to Tokyo and started drawing his manga works. In 2008, he applied for the 80th Weekly Shōnen Magazine Freshman Manga Award, where his work "Heart Break One" was given the Special Encouragement Award. His other work "orz" was chosen as a selected work in the 81st Weekly Shōnen Magazine Freshman Manga Award.