He was called "flying foreign minister" due to his active diplomacy in increasing the role of Japan when he was in office.

[3] Sonoda joined the Japanese army in 1938, and served both in China and in the Pacific area during World War II.

[5] He served as parliamentary vice-foreign minister in 1955, and actively involved in normalizing the relations between Japan and the USSR.

[12] When in office for the second time, Sonoda visited five African countries in July 1979, including Tanzania, Nigeria, Kenya, Ivory Coast and Senegal.

[17][18] Sonoda called for adopting the omnidirectional diplomacy and unlike his two predecessors, issued entry visas to Soviet economic delegations.

[19] The reason for Sonoda's removal from his post was his blunt remarks concerning U.S. policies in June 1981 as well as his other statements detrimental to Japan's relations with South Korea.

His son from the first marriage, Hiroyuki Sonoda, ran for his father seat in the Kumamoto Prefecture in the general elections of 1986.