Following philosophy and Oriental art studies at Tokyo's Waseda University, he entered films in 1941; but eight months later he was drafted into the Imperial Japanese Army and dispatched to Manchuria. In a courageous act of personal defiance, he refused promotion and remained a private for the duration of WWII. He spent the last year of the conflict as an American prisoner of war. He resumed his budding film career late in 1946 as an assistant to Keisuke Kinoshita at the Shochiku company. It wasn't until 1952 that Kobayashi turned out his first film as a director. His early films showed the influence of his mentor. But gradually he carved out his own path, and in 1959-61 asserted his mastery with a remarkable nine-hour trilogy, Ningen no Joken / The Human Condition (1959-61), a graphically vivid, uncompromising critique of the brutalities and horrors of the Second World War and their effect on the emotional lives of the participants. Thr trilogy's first part, No Greater Love, won the San Giorgio Prize at the 1960 Venice Film Festival. Kobayashi attracted wider admiration with Sepukku / Harakiri (1962), a Samurai period film many consider his masterpiece, and Kaidan / Kwaidan (1964), a harrowing anthology of ghost stories. Both of these films won the International Jury Prize at Cannes, in 1963 and 1965, respectively. Other personal triumphs in Kobayashi's sparse but rich repertoire were Joiuchi / Rebellion / Samurai Rebellion (1967) and Kaseki / Fossil (1975), the latter a tautly edited feature version of his eight-hour TV drama.