Traditionally believed to be the 17th head of the Shimazu clan, he was a skilled general during the Sengoku period who greatly contributed to the unification of Kyūshū.

[3] In 1587, facing Toyotomi Hideyoshi's troops that sought to pacify Kyūshū, Yoshihiro pressed for war even after his brother and the head of clan Yoshihisa surrendered.

In 1597, working together with Tōdō Takatora, Katō Yoshiaki and Konishi Yukinaga, Yoshihiro defeated Won Kyun's navy.

However, recent research indicated that Yoshihiro had chosen to side with Mitsunari from the very start, before Mōri Terumoto announced the declaration of war against the Tokugawa in July 1600.

Yoshihiro also played an important role as a member of Mitsunari's core staff and was pivotal in persuading Uesugi Kagekatsu to ally with them.

[5][6][7] After he beat the Shimazu forces, returned to Ieyasu to ask permission to participate on the Sekigahara main battle which planned in the next day.

Yoshihiro had his troops make a fighting retreat called Sutegamari (捨て奸), where until a certain number of men died holding a position and repelling an attack, the main body of the army fought as well.

Though Toyohisa and the bulk of the troops died, the charge and retreat were a success with a wound dealt to Ii Naomasa in the process.

The Japanese historian Shiramine Jun studied why the Shimazu clan behaved torpidly and deduced it was because Yoshihiro had become involved in the power struggling between his brother Yoshihisa and Ijūin Tadamune.

On August 23, 1918, Yoshihiro was posthumously awarded the courtesy title of senior third rank (shō san-mi, 正三位) by Emperor Taishō.