Lifespan: Daiei 5 (1525) to 4/20 of Tenbun 15 (1546)
Other Names: Gorō (childhood)
Title: Master of the Office of Palace Repairs
Father: Uesugi Tomooki
Children: Norikatsu, Norifusa
Uesugi Tomosada served as a bushō during the Sengoku period. Tomosada was the final head of the Ōgigayatsu-Uesugi family and served as the lord of Matsuyama Castle in Musashi Province.
In 1525, Tomosada was born as the son of Uesugi Tomooki, a daimyō and the head of the Ōgigayatsu-Uesugi. In the fourth month of 1537, Tomooki died so Tomosada succeeded him as the head of the family. To serve as a base from which to oppose the Gohōjō clan, he built the Jindaiji Castle on the grounds of the Jindai Temple in Fuchū in Musashi. Owing to Tomosada’s youth, however, Hōjō Ujitsuna viewed the succession as an opportunity and, in the seventh month, attacked him at Kawagoe Castle. Tomosada fled and, thereafter, resided in Matsuyama Castle.
In 1541, after many years of conflict, Tomosada reconciled with his archenemy, Uesugi Norimasa of the Yamauchi-Uesugi family (a daimyō from Shimotsuke Province), united in opposition to Hōjō Ujiyasu. In 1545, Tomosada aligned with Imagawa Yoshimoto, the sengoku daimyō of Suruga Province, to form an encirclement campaign against the Hōjō. After Yoshimoto raised arms and Ujiyasu deployed to Suruga, Tomosada, along with Norimasa and Ashikaga Haruuji (the Koga kubō), led an army of 80,000 soldiers to assault Kawagoe Castle in an event known as the Siege of Kawagoe Castle. Despite a valiant defense by Hōjō Tsunanari, the lord of Kawagoe Castle, the attacking forces nearly toppled the castle. Then, on 4/20 of Tenbun 15 (1546), Ujiyasu, after having ended the battle against the Imagawa, launched a surprise attack against the besieging forces, resulting in a major defeat for the Ōgigayatsu-Uesugi army. Tomosada was killed in action while members of the combined forces scattered in all directions. Having failed to recapture Kawagoe Castle, Tomosada died at the age of twenty-two.
There are no records concerning the circumstances of Tomosada’s death or who killed him so the possibility that he died of illness cannot be disregarded. The details of his demise remain uncertain. There is also a theory that the allied army collapsed, not as a result of the surprise attack by Ujiyasu, but rather owing to the sudden death of Tomosada.
Upon the death of Tomosada, the Ōgigayatsu-Uesugi family was extinguished. For a while, Uesugi Norikatsu from an illegitimate branch of the Ōgigayatsu attempted, with the backing of Uesugi Terutora (Kenshin), to revive the family, but eventually submitted to the Gohōjō clan.