A leader of the postwar independent film production movement. Imai was an erratically brilliant filmmaker whose controversial leftist views and "subversive" activities forced him outside Japan's studio system. He directed his first feature, "The Namazu Military Academy", in 1939 but shortly after was forced to give up politics under the wartime military regime and began making war-collaboration propaganda films.
After the war, Imai joined the Communist Party and returned to leftist themes, criticizing the corruption of the wartime leaders. In "The People's Enemy" (1946) Imai proselytized on behalf of postwar democracy. During this period he directed his greatest commercial success, "Green Mountains Part I and II" (1949), which depicted a small town high school's struggle against established institutions and values. Imai was blacklisted at times for his political views and was fired by Toho studios for leading a strike. His subsequent freelance work continued to focus on the plight of the downtrodden proletariat.