Hosokawa Harunobu served as a bushō during the Sengoku period.  He was the military governor of Izumi Province supporting Hosokawa Takakuni.

Harunobu was born as the son of Hatakeyama Hisanobu, a shugo daimyō.  Harunobu was the younger brother of Hatakeyama Tanenaga.

In the sixth month of 1507, Hosokawa Masamoto, the deputy shōgun of the Muromachi bakufu, was assassinated by Kōzai Motonaga and Yakushiji Nagatada, supporters of Hosokawa Sumiyuki, in an event known as the Lord Hosokawa Incident (Hosokawa-dono no hen).  This gave rise to a prolonged succession struggle for control of the Hosokawa-Keichō family among his three adopted sons:  Hosokawa Sumiyuki, Hosokawa Sumimoto, and Hosokawa Takakuni.  This is known as the Conflict between the Hosokawa (Ryō-Hosokawa no ran) and, more broadly, as the Eishō Disturbance (Eishō no sakuran).  In Izumi Province, the role of the military governor split between those in Takakuni’s faction and those in Sumimoto’s faction.

In 1523, after Hosokawa Takamoto, the military governor of Izumi in Takakuni’s faction, fell ill, Harunobu and the junior military governor, Hosokawa Katsumoto, succeeded Takamoto.  In the era of Harunobu’s father, Hisanobu, the Hatakeyama-Bishū family (descended from Hatakeyama Masanaga) provided official recognition to the shrines and temples in Izumi to the rights to their landholdings.  Harunobu’s appointment to the role of military governor of Izumi is surmised to have connections to the affinity between the Hatakeyama clan and Izumi Province.

In the tenth month of 1524, Harunobu engaged in a battle against Hosokawa Mototsune, the military governor of one-half of Izumi in Harumoto’s faction, at Hishiki in the Ōtori District of Izumi.  In this battle, Harunobu was defeated and, according to one account, the whereabouts of Kōzai Motomori were temporarily unknown.  The defeat by Motomori of Hatakeyama Yoshitaka (who acted in concert with Harumoto’s faction by rebelling in Kawachi Province) caused the fall of Harumoto’s faction.  Mototsune appears to have retreated to Awa Province.

After the first month of 1526, Harunobu disappears from historical records.  He may have fallen into ruin or been killed at the Battle of Katsurakawara in the second month of 1527.

In the sixth month of 1531, in an event known as the Collapse at Daimotsu, Takakuni was defeated and killed by the forces of Hosokawa Harumoto.  During this event, the governor of Izumi was also killed.  Meanwhile, Katsumoto continued to operate after this time so the reference appears to be in regard to Harunobu or his successor.