Amago Toyohisa served as a bushō and was a family member of the Amago clan.  He was the second son of Amago Kunihisa.

In 1524, Toyohisa was adopted into the family as a son-in-law as a condition for support from the Amago clan in an effort by Mototsuna to contest the appointment of his older brother, Mōri Motonari, to become successor to Mōri Kōmatsumaru as head of the Mōri clan.  Mototsuna was killed in an attack ordered by Morinari on Mototsuna’s home base at Funayama Castle so he failed to realize his ambitions.

In 1546, Nanjō Sōshō, lord of Ueshi Castle and a kokujin in Hōki Province, raised arms with support from Takeda Kuninobu, a senior retainer of the Yamana clan in Inaba Province and toppled Kawaguchi Castle.  Situated on the borders of Hōki and Inaba provinces, Kawaguchi had been occupied by the Yamana.  Amago Akihisa responded by ordering the deployment to Hōki of 6,000 men under the command of Toyohisa and Amago Kunihisa from the shingūtō band of elite fighters.  Kunihisa set-up an encampment on the western shore of the Hashizu River to oppose the allied forces of the Nanjō and Takeda.  At the Battle of Hashizugawa, Toyohisa led 700 mounted soldiers against the enemy position, but fell from his horse after an arrow pierced his chest armor, whereupon he was killed by Nakahara Mokunojō, a follower of the Takeda.

Upon hearing news of the loss, Kunihisa counterattacked, killing Takeda Tsunenobu and causing Nanjō Sōshō to flee.