He was a Uhyoenojo (high officer of the Imperial Guard). Following Tomomori Taira, he participated in the routing of Yukiie Minamoto's forces at Sunomata, Mino Province (Gifu Prefecture) (1181).
Accompanied Koremori Taira in his campaign against Yoshinaka Kiso at Mt. Tonami (1183), killing Yoshikiyo Ashikaga, a general of Kiso. After the Tairas were annihilated in the Battle of Yashima (1185), he hid in Kyoto. When Tomotada Taira, son of Tomomori, planned to raise an army against the Minamotos, he participated in the plan. When the Minamoto's learned of the plot Tomotada killed himself and Moritsugu fled. Finally was captured and decapitated on Yuigahama Beach at Kamakura.