Minagawa Toshimune served as a bushō during the Sengoku period. He was the lord of Minagawa Castle in the Tsuga District of Shimotsuke Province. He used the names of Yamashiro-no-kami and Danjō-no-chū.
Toshimune was born as the son of Minagawa Shigekatsu. Toshimune received one of the characters in his name from Utsunomiya Toshitsuna and adopted the name of Toshimune. During the Tenbun era (1532 to 1555), he inherited the headship of the clan, joined forces with Hōjō Ujiyasu, sought independence and fought against Utsunomiya Hirotsuna, but lost and surrendered.
Later, he increased his voice within the Utsunomiya family, and, based on some theories, exceeded the influence of Haga Takatsugu as the holder of real authority in the family. In 1572, he took advantage of the illness of his lord, Hirotsuna, to occupy Utsunomiya Castle, murder a senior retainer named Okamoto Sōkei, and, together with the Nasu and Hōjō clans, seize control of the family.
In his later years, Toshimune transferred headship of the clan to Hirokatsu and adopted the monk’s name of Shintetsu. There is a theory that Toshimune, together with Yūki Harutomo, headed out to support Yanada Harusuke and his son at Sekiyado Castle under assault by Hōjō Ujiyasu and was killed in action. In fact, however, around the ninth month of 1573 when Toshimune is thought to have died, it has been confirmed that the Minagawa and Mibu clans rebelled against the Utsunomiya clan and attacked the Oyama clan (who supported the Utsunomiya) at 粟志川 Castle. Toshimune appears to have died at this time.