Ninth head of the Ouchi clan. He succeeded his father Hiroyuki as clan head in 1352. From around 1355 he advanced into Nagato Province, repeatedly clashing with Koto Yoshitake, 17th head of the Koto clan and shugo of Nagato. In January 1358, Hiroyo captured and destroyed Shimofuri Castle, the Koto stronghold, driving Yoshitake to flee to Kyushu. By the sixth month of the same year he had also taken Chofu, completing his conquest of Nagato. He was confirmed as shugo of Suo and Nagato by both the Northern and Southern Courts and moved his base to Yamaguchi, laying the foundation for the city later called the "Kyoto of the West." He died in 1380.

A strategist who skillfully exploited the split between the Northern and Southern Courts, expanding his power through pragmatic political judgment that secured shugo appointments from both.

His capture of Shimofuri Castle completed the pacification of Nagato Province, cementing the foundation of Ouchi rule over Suo and Nagato. His relocation of the clan base to Yamaguchi laid the groundwork for the city later celebrated as the "Kyoto of the West."