Ihara Tadayori served as a bushō during the Sengoku period. He was a retainer of the Imagawa clan based in Suruga Province. Ihara Tadatane, the lord of Ihara Castle, was his brother-in-law.
Tadayori originated from the Ihara clan. Initially, he served Imagawa Yoshimoto. In 1560, he participated in the Battle of Okehazama during which Yoshimoto was killed in a lightening attack by Oda Nobunaga. Yoshimoto was succeeded by his lineal heir, Imagawa Ujizane. Tadayori served Ujizane and resisted an invasion of Suruga by Takeda Shingen in 1568. He remained loyal to the Imagawa family to the end.