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 and in the Tojo Cabinets (from 1941 to 1944 for the latter). In these positions, he allegedly took part in the formulation of the aggressive policies of Japan and in the financial, economic and industrial preparation of Japan for the execution of those policies.
Okinori Kaya also held other responsibilities in different companies. Thus, he was President of the North China Development Company. He was accused to have personally benefited from that position and to have eased drug smuggling in China.
He was captured in 1945 in order to be tried by the International military tribunal for the Far East.
