Born into the court noble Saionji family, he was a politician active as a genrō (supreme national advisor) from the Meiji through Shōwa periods. Familiar with European culture from childhood, he studied in France for ten years in his youth, learning French, law, and political science. After returning to Japan he participated in the Meiji government and held posts including Minister of Education and Foreign Minister. As successor to Ito Hirobumi's Rikken Seiyukai, he served twice as Prime Minister (1906-1908, 1911-1912). He supported Taisho Democracy and contributed to the development of party government and liberalism. At the Paris Peace Conference after World War I (1919), he participated as the chief of the Japanese delegation. From 1924 onward, as the last genrō, he single-handedly bore the responsibility of recommending (to the Emperor) the appointment of Prime Ministers, working for political stability. He was opposed to military intervention in politics and resisted the militarist trends of the 1930s. However, through the May 15 and February 26 Incidents his political influence gradually declined. He died in 1940 at his villa in Okitsu (present-day Shimizu Ward, Shizuoka City, Shizuoka Prefecture). He died at 91.

A rare politician combining aristocratic refinement with liberal political thought. While devoted to French culture and an elegant lifestyle, he consistently protected his political convictions without being swept away by the currents of the times.

As the last genrō, he contributed to political stability in the Taishō and early Shōwa periods. His stance as a liberal politician resisting the rise of the military is appreciated today. The site of his former villa in Shimizu Ward, Shizuoka, is known as a historical site.