After the Meiji Restoration, he was sent to France for studies, and on his return to Japan served in the War Ministry. Later, he served as director of the Cabinet Gazette Bureau, Secretary of the Cabinet Legislation Bureau and other posts, in 1890 he became the first Chief Secretary of the House of Representatives the Diet of Japan.
Sone was elected to the House of Representatives in the 1892 Japanese general election, and served as Vice-Speaker of the House in the same year. In 1893, he became Japanese ambassador to France and negotiated the revision of the unequal treaties between France and Japan.