Oka Gōsuke served as a bushō during the Sengoku and Azuchi-Momoyama periods. He was a retainer of the Bizen-Ukita clan.
Gōsuke was known as a handsome young man and had a fief of 700 koku.
According to military chrinicles from later eras, in 1561, upon orders of Ukita Naoie, he entered the family of Saisho Mototsune, the lord of Tatsunokuchi in the Jōtō District of Bizen Province, assassinated Mototsune and returned to the Ukita. At this time, he was referred to as Oka Kiyosaburō so it is surmised this occurred during his youth and prior to his coming-of-age ceremony. Based on other accounts from the period, Mototsune was killed in a plot orchestrated by the Mōri clan.
Gōsuke served in the Battle of Myōzenji in 1567 and the Siege of Kōzuki Castle in 1578. In 1579, after the Ukita clan cut ties with the Mōri clan and colluded with the Oda, the environs of Bitchū-Shinobuyama Castle defended by Gōsuke became a flashpoint for frequent clashes with the Mōri.
In 1581, the Mōri army led by Mōri Terumoto commenced in earnest an assault against Shinobuyama Castle where Gōsuke and Ukita Shinano-no-kami (Ukita Gengorobei, the son of Ukita Gorōzaemon) were based. First, Kikkawa Tsunenobu (later known as Kikkawa Hiroie) was sent in the vanguard to fight against Gōsuke and Shinano-no-kami. Next, after the arrival of reinforcements for the Ukita, Tsunenobu (who had been observing the situation) quickly began a withdrawal, but Gōsuke and other members of the garrison burst out of the castle in pursuit. Tsunenobu responded by calling upon soldiers in a nearby division to attack, causing the pursuing forces to collapse from the rear, whereupon they were forced to return to the castle. Tsunenobu followed-up by burning down the area below the mountain and surrounding the Shinobuyama Castle. That night, he set fire to the castle and, in the midst of continuing attacks, the defenders fell into chaos as the castle was toppled. Ukita Shinano-no-kami and his lineal heir, Magoshirō, were killed in the course of a major defeat.
Gōsuke is also deemed to have died during this battle, but there is no clear account of his demise. There is a battle memorial of Oka Gōsuke in the environs of Shimoashimori in the Kita ward of the city of Okayama in Okayama Prefecture so the circumstances of his demise remain a mystery. There are various theories in military chronicles including, in particular, the year of Tenshō 7 (1579). One account refers to this as the year of the Siege of Shinobuyama Castle, while records from the Mōri clan refer to a battle in Yose in Tenshō 7 (1579) and the Siege of Shinobuyama Castle in Tenshō 9 (1581). These records are given more weight than the chronicles based on certificates of commendation given by Mōri Terumoto and Kikkawa Motoharu to their retainers in this series of battles. The current view is that certain chronicles confused the battle that occurred in the environs of Yose with the subsequent Siege of Shinobuyama Castle.