After graduating from the philosophy course of Tokyo Imperial University, he applied himself to the study of Marxism and Indian thought. While pursuing these studies, he supported himself by editorial work for the magazine Michi headed by Matsumura Kaiseki and by doing translation jobs for the General Staff Office of the army.
In 1918 he took a position in Tokyo with the South Manchuria Railway. He served as head of the research section of the company’s East Asia Economic Research Bureau and later as head of the bureau itself, and when the bureau separated from the company and became an independent organization, he became its director.
From 1920 on, he also held a position as professor of Takushoku University in Tokyo, lecturing on the history of colonialism. In 1926 he was awarded the degree of Doctor of Law for his study of the system of chartered colonial companies, a study that was said to have been highly praised by the eminent political scientist Yoshino Sakuzo.
Meanwhile, Ôkawa was forming close connections with a number of middle-ranking army officers. In 1931 he joined with Lieutenant Colonel Hashimoto Kingorô and other officers to form a secret society known as the Sakurakai (Cherry Society) and began planning a military coup d’état. The plans were scheduled for execution in March of 1931, and again in October, but in both cases were called off or failed to be carried out. In 1932, Ôkawa reorganized and expanded the right-wing group Kochisha, reestablishing it as the Jimmukai with himself as its head. He called for the liberation of all nonwhite peoples and the moral unity of the world, preaching a kind of overall Asian nationalism that was strongly colored by national socialism. He thus came to rank beside Kita Ikki as one of the leading thinkers of the fascist movement in Japan in the thirties.
Ôkawa had only indirect connections with the May 15th incident of 1932, when a group of young naval officers and army cadets carried out various attacks and assassinations, but he was arrested nevertheless and condemned to five years’ imprisonment. He was released in 1937 as the result of a general amnesty. He worked to drum up support for Japan’s war effort in China and, after the outbreak of the Pacific War, enthusiastically advocated the establishment of what was known in the national slogans of the time as “the new order in Greater East Asia.” For this purpose he wrote treatises such as that entitled Daitôa shin chitsujo no rekishiteki seikaku ( “The Historical Character of the New Order in Greater East Asia”) and also took pains to expound his ideas in academic circles.
After Japan’s surrender, he was arrested as a first-class war crimes suspect, but at the public trial held before the International Military Tribunal for the Far East, he slapped one of the other defendants, the former prime minister and general of the army Tojo Hideki, on the head. He was excused from the trial on grounds of mental disorder and was confined to a hospital. Later the charges against him were dropped and he was set at liberty. He devoted his last years to translating the Koran into Japanese. In addition to the works already mentioned, he was the author of Kinsei Toroppa shokuminshi and other works.
He began to advocate a type of national revolution that had strong fascist overtones, and in 1919 he joined with Kita Ikki and Mitsu- kawa Kametarô to form the Yüzonsha (Society for the Preservation of the National Essence). In addition to putting out Nihonjin, the society’s official magazine, he published a number of pamphlets, devoting himself to the spread of nationalistic ideas.