- Born: 1517?
- Died: 1582
- Sons: Nanbu Harutsugu (d. 1582), Nanbu Nobunao (adopted)
- Distinction: Mutsu warlord
Harumasa was a son of Nanbu Yasunobu and succeeded him in 1540. He was granted the use of 'Haru' in his name from the shôgun Ashikaga Yoshiharu in 1539. He attacked the Tozawa clan to the south and captured Iwate district. In the late 1550's he went to war with the Akita family of the Ugo region. His effective leadership and rapid attacks assured the Nanbu a status as one of the most powerful clans in northern Mutsu province. In 1581, however, he suffered the rebellion of the Ôura (Tsugaru). He was succeeded by his son Harutsugu, but as the latter died soon afterwards, Harumasa's adopted son and nephew, Nobunao, was named the heir.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005