Sadamasa was a son of Hatakeyama Harima no kami Masayori and the nephew of Hatakeyama Takamasa. He was encouraged by Kennyo Kosa to revolt (in conjunction with Matsunaga Hidahide) against Oda Nobunaga in 1577. He later joined the alliance (headed by Tokugawa Ieyasu) against Toyotomi Hideyoshi in 1584 but was killed in the fighting. Sadamasa's descendants went on to serve the Tokugawa clan.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005