As Prince Hirotada died without heirs, the Kachō-no-miya household became extinct.

Prince Hironobu was appointed to perpetuate the Kachō name, in order to ensure that the proper familial and ancestral rites were performed, but his status was devolved in December 1926 to the peerage title of marquis (kōshaku) under the kazoku peerage system.

He served his midshipman tour on the cruiser Iwate, and as a sub-lieutenant on the battleship Yamashiro.

He subsequently served as chief torpedo officer on the destroyers Akebono and Sazanami, rising to the rank of commander.

Kachō Hironobu married Kan’in Hanako (1909–2003), 5th daughter of Prince Kan'in Kotohito, but they subsequently divorced.