Nanbu Masayasu served as a sengoku daimyō of Mutsu Province from the late Muromachi to Sengoku periods.  He was the twenty-second head of the Nanbu clan.

Masayasu was born as the second son of Nanbu Nobutoki, the twenty-first head of the Nanbu clan and older brother of Nanbu Nobuyoshi.

Masayasu received one of the characters in his name from Ashikaga Yoshimasa, the eighth shōgun of the Muromachi bakufu.  Similar to his father and younger brother, there is a scarcity of recorded details concerning their lives.  Nevertheless, his five sons contributed to the centralization of power by the Nanbu enabling them to become a sengoku daimyō family.

The year of his demise is unknown, but his name appears on signs dating to the Eiroku and Tenshō eras that were staked to a building’s ridgepole at construction time stating information such as the building’s donor, builder, date, and reason for construction.​