[2] Tadatsune was originally a resident of Nitta, Izu Province (present-day Kannami, Shizuoka Prefecture).

[2][3] In 1180, he joined Minamoto no Yoritomo's troops, and played an active part in the punitive expedition of the Taira clan in the West.

Tadatsune joined the fight late, criticized the poor strategy of the samurai and told them to separate the two brothers and surround them.

[2][3] Enraged by this, Yoriie ordered Tadatsune and Wada Yoshimori to assassinate the mastermind of the incident, Hōjō Tokimasa.

On the other hand, Tadatsune's ambiguous behavior was deemed suspicious and caused Tokimasa's brother Hōjō Tadatoki to misinterpret Tatatsune's intentions.

Following this on October 12, 1203, Tadatsune was killed by Katō Kagekado on behalf of the Hōjō clan, caused by Tadatoki's misunderstanding.