He was appointed a Councilor of the Manchurian Affairs Bureau in 1936. Between 1937 and 1944 he held different positions at the Ministry of Finance of Japan, among which that of Finance Minister in the Konoye government then in the Tojo government from 1941 to 1944. In this position, he was alleged to have taken part in the formulation of the aggressive policies of Japan and especially in Japan’s financial, economic and industrial preparation for the execution of such policies.
Okinori Kaya also held other responsibilities in various companies. For example, he was President of the North China Development Company and in this position he was accused of having personally benefited by the easing of drug smuggling to China.
He was captured in 1945 and tried by the International Military Tribunal for the Far East.