With his elder brother, Yoshihisa, he conquered almost all of Kyushu and defied orders of Hideyoshi Toyotomi. Surrendered to Hideyoshi when his forces attacked Kyushu (1587). Hideyoshi made him iord of Osumi Province (Kagoshima Prefecture).
In Hideyoshi's Korean campaign, he, together with Muneshige Tachibana and Yoshitomo So, defeated Chinese naval forces under Chen-Rin and enabled the Japanese expeditionary army to retreat from Korea safely.
In the Sekigahara Battle (1600), he sided with Mitsunari Ishida and was defeated by the East Camp and retreated to osumi by sea from Sakai near Osaka. Ieyasu pardoned him and permitted him to keep osumi. Yoshihiro retired in favor of Iehisa, his son.