Head of the Nanbu clan, based at Sannohe in Mutsu Province (now Sannohe-cho, Aomori Prefecture). The Nanbu were a prestigious daimyo house whose fierce mounted warriors were said to number 'eighty thousand,' and they held dominion over vast territories across northern Mutsu and the northeastern part of Japan. Through patient perseverance he overcame the internal power struggles within the clan—including rivalry between the Sannohe Nanbu and the Kunohe Nanbu—to establish his position as head of the family and achieve internal unity. He attended Toyotomi Hideyoshi's Oshu settlement of 1590 and had his domain (Nubefu, Kazuno, Iwate, Hei, Kunohe, and others) formally confirmed. The following year, 1591, the powerful clansman Kunohe Masazane rose in rebellion, claiming he was the rightful Nanbu heir (the Kunohe Rebellion). Hideyoshi ordered an army of over 60,000, including forces under Gamo Ujisato and Asano Nagamasa, to suppress it. After the rebellion was pacified, Nobunao relocated his base from Sannohe to Morioka and began constructing Morioka Castle—the origin of the 100,000-koku Morioka domain of the Edo period. His achievement in laying the foundations for the Nanbu clan's survival and development across northern Tohoku was enormous.

A pragmatic leader who overcame internal rebellion and preserved the Nanbu clan through cooperation with the Toyotomi regime. He valued political judgment over brute force and had the wisdom to navigate a turbulent age.

He initiated the construction of Morioka Castle and laid the foundation of the 100,000-koku Morioka domain. Thanks to his decisions, the Nanbu maintained good relations with the Toyotomi and Tokugawa regimes and survived as lords of Morioka until the Meiji era. The suppression of the Kudo Rebellion is seen as a pivotal event in establishing central authority over northern Tohoku.