Haruno Okubo studied at the Military Preparatory School, then for five years in France.
Haruno Okubo was an artillery unit commander in the Imperial Guard Forces (1868). After returning to Japan, he was promoted to major, then became director of the Toyama Military School. Took part in the Sino-Japanese War (1894-1895) as commander of the Seventh Brigade in the Second Army. Commanded a brigade which fought in Formosa. In the Russo-Japanese War (1904-1905), he was commander of the Sixth Division, Fourth Army.