Kojima Motoshige served as a bushō during the Sengoku and Azuchi-Momoyama periods. Motoshige was a retainer of the Jinbō and Uesugi clans. He served as the chamberlain for Hinomiya Castle in the Imizu District of Etchū Province.
Motoshige was a senior retainer of Jinbō Nagamoto, a daimyō in Etchū. During the Kyōroku era (1528 to 1532), Motoshige engaged in negotiations with the Asakura clan of Echizen Province, supporting Jinbō Nagamoto‘s efforts to revive the Jinbō family so he is surmised to have been a clan elder. However, after the Jinbō were defeated by the Uesugi, he supported the Uesugi family, coming into conflict with Terashima Motosada, the leader of the faction aligned with the Ikkō-ikki and the Takeda clan of Kai. Motoshige then expelled them and seized authority in the Jinbō family. After the demise of Nagamoto, the family became retainers of the Uesugi while Motoshige performed an important role as the head of the Etchū group.
In the fifth month of 1572, after the Kaga Ikkō-ikki raised arms and invaded Etchū, Motoshige holed-up in Hinomiya Castle to fight back against the attacking forces, but before the arrival of reinforcements led by Sanponji Sadanaga of the Uesugi army, Motoshige surrendered and vacated the castle in a conflict known as the Battle of Shiritarezaka. At the crossing point on the Jinzū River, the Uesugi army endured a surprise attack by the ikki forces, incurring many losses. After endeavoring to explain the situation, Motoshige was treated well by the Uesugi and, after the death of Uesugi Kenshin, received a long sword from his estate.
In the third month of 1582, during the Conquest of Kōshū, Motoshige acted in concert with Takeda Katsuyori who faced precarious circumstances. Acting together with Karōdo Chikahiro, Motoshige pierced through the flank of the Oda army during a siege of Uozu Castle for a lightening assault against Toyama Castle. He incarcerated the Jinbō Nagazumi (the eldest son of Jinbō Nagamoto) but was suppressed by members of the Oda army commanded by Shibata Katsuie. As a member of the Uesugi army, he resisted the pacification of Etchū by Sassa Narimasa, but his subsequent whereabouts are unknown and is considered to have died soon thereafter. His descendants are believed to have been members of the Toyama domain in Etchū in the Edo period.