Sogō Masayuki served as a bushō during the Azuchi-Momoyama period. He was a member of the Miyoshi clan and illegitimate child of Sogō Kazumasa. He was first called Kazuchika and then Miyoshi Naganori. Masayuki held the title of Senior Eighth Rank (Upper), Assistant to the Imperial Guards. His older brother was Miyoshi Yoshitsugu, the final head of the Miyoshi clan.
Masayuki served as the chief retainer for Sogō Masayasu who was adopted by Kazumasa. Masayuki is regarded to have been older than Masayasu. When Masayasu affiliated with Oda Nobunaga, Masayuki followed him and fought against Chōsokabe Motochika, the sengoku daimyō of Tosa Province. After the unexpected death of Nobunaga on 6/2 of Tenshō 10 (1582), the Sogō were subject to a ferocious attack by the Chōsokabe army which left Masayasu fleeing in defeat.
On 8/6 of Tenshō 10 (1582), the combined forces of the Chōsokabe and the Kagawa clans attacked Fujio Castle where Kōzai Yoshikiyo was holed-up, but, through the mediation of Kagawa Yukikage, Yoshikiyo surrendered to Kagawa Chikakazu’s army. Bolstered by Yoshikiyo’s battalion of 1,000 soldiers, on 8/11, Chikakazu’s army totaling 11,000 troops departed from the Kokubun Temple (affiliated with the Uomuro faction of the Shingon sect) in Sanuki and surrounded Sogō Castle. This event is known as the First Siege of Sogō Castle.
At the time, Sogō Masayasu was in Shōzui Castle with Masayuki serving as the chamberlain to defend the castle. Nevertheless, upon receiving news of the siege by an army of over 10,000 soldiers, Masayuki anticipated a prolonged conflict, so he reduced the size of the garrison to 1,000 soldiers, stored three months worth of provisions, and prepared to hold-out against the besieging forces. Despite a lengthy siege, the castle did not fall. With the onset of the winter season, a unit was left to keep watch on the castle while the remainder of the Chōsokabe forces returned to Tosa and the First Siege of Sogō Castle came to an end.
In Tenshō 14 (1586), Masayuki joined a Toyotomi army led by Sengoku Hidehisa to invade Bungo Province in northeast Kyūshū. On 12/12 of the same year, Masayuki, along with Sogō Masayasu, were killed in action at the Battle of Hetsugigawa after Hidehisa made an ill-fated decision to order his army to cross the Hetsugi River to attack the Shimazu forces before the arrival of reinforcements.