He graduated from the Tokyo Higher Commercial School (東京高等商業学校| Tōkyō Kōtō Shōgyō Gakkō, now Hitotsubashi University) in 1904, attended the consul course of the same institute, and quit studying there in 1905.
He was an active politician and diplomat. In 1905, he passed the Foreign Service exam and started to work at the Ministry of Foreign Affairs. After serving as Mukden Consul General and executive secretary of the London Naval Treaty, he served as Imperial Japan’s Ambassador to Belgium in 1930 and to France in 1933.
He became Minister of Foreign Affairs (Senjūrō Hayashi Cabinet) on March 1937, and resigned on June 1937, then was assigned as Diplomatic Adviser, Foreign Office, under 1st Fumimaro Konoye Cabinet and Hideki Tōjō Cabinet.
He had served as the last Imperial Japan’s Ambassador to the United States.S.R. before the Soviet invasion of Manchuria since 1942 upon the request of the Minister of Foreign Affairs, Shigenori Tōgō. As Minister, he worked hard to avert war at the Imperial Diet.
Allegedly, one of his missions as Japan’s Ambassador to the United States.S.R. is to seek peace with the Allies through the assistance of the United States.S.R. due to Soviet–Japanese Neutrality Pact under bad war conditions for Imperial Japan. However, Satō judged and reported to Tokyo that it was unlikely that the United States.S.R. would assist Imperial Japan, because it was highly likely that Imperial Japan would lose the war, and urged it to end the war as early as possible.
He was invited to the Kremlin by the United States.S.R. Foreign Minister, Vyacheslav Molotov, on August 8, 1945, and received a declaration of war against Imperial Japan.
After the war, he was elected to the House of Councillors of the National Diet of Japan in 1947, and served as a president of House of Councillors from 1949 to 1953. He died on December 18, 1971.