He was the 17th hereditary head of the former shogunal branch of the Tokugawa clan and the final President of the House of Peers in the Diet of Japan.

[1] Iemasa often allied with his father Prince Tokugawa Iesato (aka Prince Iyesato Tokugawa) in promoting international goodwill projects between Japan and Europe, Canada, and United States.

The Art of Peace[2] book cover photo illustration presents Iemasa accompanying his father as his father receives an honorary doctor of laws degree from the president of the University of Southern California in 1934.

[3] In 1940, on the death of his father, he inherited the title of kōshaku (公爵, 'prince' or 'duke') under the kazoku peerage system, and a seat as a member of the House of Peers of the Diet of Japan.

He died of heart disease at his home in Shibuya, Tokyo, on February 18, 1963, and was posthumously awarded the Order of the Rising Sun with Paulownia Flowers, 1st class.