Born in February 1566 at Kakunodate Castle as the son of Tozawa Michimori, 16th head of the Tozawa clan. In 1578, at just 13, he inherited the headship in place of his sickly elder brother and became lord of Kakunodate Castle. In 1583 he defeated Ando Chikasue at the Battle of Karamatsuno, retaking Yodogawa Castle, and in 1586 he captured Numadate Castle at the Battle of Ageno, growing into a warrior feared as "Oni-Kuro" (Demon Kuro) who ruled 44,300 koku in Kitaura district. In 1590 he joined Toyotomi Hideyoshi's Siege of Odawara and had his domain confirmed after an audience with Hideyoshi on March 10, but died of illness in camp before the castle fell, at age 25.

A precocious warrior who inherited leadership at 13 and earned the fearsome nickname "Demon Kuro" through repeated battlefield successes.

From his base at Kakunodate Castle he established the Tozawa as a full-fledged sengoku daimyo in Kitaura. His early death at 25 was much lamented; his successor Tozawa Masamori was later transferred to Matsuoka and then Shinjo domain.