Ninomiya Nagatsune served as a bushō during the Sengoku and Azuchi-Momoyama periods.  Nagatsune was a kokujin, or provincial landowner, in Etchū Province.  He served as a retainer of the Jinbō and Uesugi clans and as the lord of Kamikumano Castle in Etchū.

Although not certain, Nagatsune may have been a descendant of Ninomiya Enna who moved to Etchū to serve as a retainer of Shiba Yoshiyuki, a shugo daimyō during the Nanboku and Muromachi periods in the latter half of the fourteenth century.  The Ninomiya clan were kokujin based in Wakasugi in the Niikawa District of Etchū. During the Sengoku period, the clan operated from Kamikumano Castle.  As Jinbō Nagamoto expanded his influence, the Ninomiya came under his command.  Owing to his military contributions during a conflict within the Jinbō family, in 1569, Nagamoto granted the former territory of Jinbō Ujiharu to Nagatsune.  Nevertheless, after the Jinbō clan separated from the Uesugi clan, Nagatsune abandoned the Jinbō in favor of the Uesugi.  In 1573, for contributions in attacks against Toyama Castle, Uesugi Kenshin granted Nagatsune the former territory of the Jinbō clan and Nagatsune received one of the character in his name from Kenshin.

In 1578, Kenshin died suddenly and, after Jinbō Nagazumi invaded Etchū with the support of the Oda, Nagatsune complied so that the rights to his territory were recognized.  At the same time, however, he also colluded with the Uesugi clan and obtained a written recognition of his rights from Uesugi Kagekatsu as well.  Thereafter, he was attacked by Saitō Toshiharu and went into seclusion in the Ino Valley on the border of Hida and Etchū provinces.  His son, Ninomiya Hidesada, was a kokujin in Echigo Province and became an adopted son of Ayukawa Morinaga.