Adopted by Yoshimaro Sato, a diplomat. His pre-adoption name was Tanaka. He graduated from Tokyo Koto Shogyo Gakko (Tokyo Higher Commercial School) (later Hitotsubashi University) in 1904. He joined the Ministry of Foreign Affairs the following year. He served as the Consul-General of Harbin in 1917 and the envoy extraordinary and plenipotentiary in Poland in 1923. He became the chief of the Japan Office of the League of Nations in 1927 and participated in the Geneva Naval Conference on Disarmament as the suite of commissioner plenipotentiary. He served as attendant in the suite of commissioner plenipotentiary (Secretary-General) at the London Naval Conference on Disarmament in 1929 and the ambassador extraordinary and plenipotentiary in Belgium in 1930. In protest against the resolution to deny the foundation of Manchukuo in the extraordinary general meeting of the League of Nations in 1933, he walked out together with Yosuke Matsuoka and other members. He was appointed the ambassador extraordinary and plenipotentiary in France the same year. He served as the Minister of Foreign Affairs in the Hayashi Cabinet in 1937. He was appointed ambassador extraordinary and plenipotentiary in the USSR in 1942. Near the end of the war, he offered his opinion to end the war to Togo, the Minister of Foreign Affairs. He served as privy Councillor in 1946. He was elected a member of the House of Councillor s in 1947 and belonged to Ryokufu-kai. He served as the chairman of the House of Councillors in 1949. In addition, as the president of the Association of the United Nations, he made efforts for Japan to join the United Nations.