Gamō Satoyasu served as a bushō during the Sengoku and Azuchi-Momoyama periods. His common name was Shirōbei. Satoyasu became the chief retainer of the Gamō clan.
He first adopted the name of Akaza Hayato and served the Rokkaku clan of southern Ōmi Province. After the fall of the Rokkaku, Satoyasu became a rōnin, or wandering samurai, and, later, served Gamō Ujisato. Satoyasu was cherished by Ujisato, serving as the lord of Naganuma Castle with a fief of 35,000 koku in the Iwase District of Mutsu. Meanwhile, during the era of service under Ujisato, Satoyasu maintained friendly relations with Ishida Mitsunari, the closest retainer of Toyotomi Hideyoshi.
In 1582, after the coup d’état against Oda Nobunaga known as the Honnō Temple Incident, upon orders of Ujisato, he protected members of Nobunaga’s family and entered Hino Castle in the Gamō District of Ōmi. In 1587, he served meritoriously in the Subjugation of Kyūshū led by Toyotomi Hideyoshi, and was later permitted to use the Gamō surname, adopting the name of Gamō Satoyasu. He followed the Gamō clan during their transfer to Aizu in Mutsu Province, becoming the chamberlain of Inawashiro Castle.
Later, Satoyasu then became the lord of Yonezawa Castle (under the command of the Gamō clan) with a fief of 70,000 koku in the Okitama District of Dewa Province. This was the largest fief held by a member of the Gamō clan. While Satoyasu served as a magistrate for criminal affairs, Machino Shigeyori and Tamai Teiyū served as magistrates to affix seals on official communications.
During the Kasai-Ōsaki Uprising and the Revolt of Kunohe Masazane in 1591, Satoyasu joined Machino Shigeyori to fight as commanders of the second battalion. From around the time that Ujisato received an increase to his fief, Satoyasu served as the leader of the magistrates to implement the policies of the Toyotomi administration in the northern provinces, making him the chief retainer in the Gamō family. While Ujisato was away in Nagoya to support the Bunroku Campaign on the Korean Peninsula, Satoyasu invited an explosive situation vis-à-vis other senior retainers, such Gamō Satoyoshi and Gamō Satonari, in Aizu, causing conflict among many members of the family.
In 1595, Gamō Ujisato died and was succeeded by his son, Gamō Hideyuki. Satoyasu then monopolized political affairs, breeding dissatisfaction among other clan members and triggering confrontation with Gamō Satoyoshi and Gamō Satonari. Satoyasu called Hachiemon to Aizu-Wakamatsu Castle (or, according to another theory, the residence of the Gamō in Kyōto) and slayed him with a sword on the grounds that this was commanded by the lord. This enraged others including hereditary retainers such as Machino Shigeyori who, seeking to assassinate Satoyasu, gathered forces, further escalating tensions between the factions. Satoyasu was censured by Toyotomi Hideyoshi and ousted from the Gamō family, after which he came under the custody of Katō Kiyomasa. Initially, through the offices of Tokugawa Ieyasu, Ishida Mitsunari was intended to take custody of Satoyasu, but Hideyuki shunned Mitsunari so Satoyasu was sent to Kiyomasa instead. The conflicts within the clan during this period are known as the Gamō Disturbance.
Satoyasu was said to have been a Christian convert so, at a later time, was assigned to Konishi Yukinaga, a Christian daimyō. In 1600, at the Battle of Sekigahara, Satoyasu served for the Eastern Army. During an attack against Katō Kiyomasa at Uto Castle, Satoyasu was either killed in action or captured and later killed. Historical accounts of the Konishi clan do not confirm the circumstances of his demise.