Saga Domain
Naomasa was born the 17th son of Nabeshima Narinao, the 9th "daimyō" of Saga Domain. His mother was a daughter of Ikeda Harumichi. His wife was the 18th daughter of "shōgun" Tokugawa Ienari, and one of his concubines was the 19th daughter of Tokugawa Narimasa.