The son and successor of Harumune, a successful kokujin lord, Terumune was officially named the 16th head of the clan by Shogun Ashikaga Yoshiteru, who awarded him the character 'Teru' in his name. Ascending to his position at the age of 17, Terumune expanded from Yonezawa-jo to rule over 30 districts. In 1584, Terumune retired in favor of his eldest son Masamune. Masamune continued the war with the Date's perennial enemy, the Hatakeyama, prompting Hatakeyama Yoshitsugu to call on Terumune to interceed. Yet, rather then talk peace when they met, Yoshitsugu actually kidnapped Terumune at sword-point. Masamune caught up with the group before they reached Hatakeyama's castle, and in the ensuing struggle Terumune was killed.
Terumune is also remembered for his correspondance with Oda Nobunaga, who sent him a number of letters after 1574 and curried his favor as an ally in the far north.