Third son of Taira no Kiyomori who became de facto head of the Taira after the death of heir Shigemori. His mother was Kiyomori's principal wife Tokiko (Nii no Ama). When Kiyomori died in 1181, Munemori led the clan against the Minamoto but lacked military talent. Forced from the capital in 1183 by Kiso Yoshinaka, he fled west with Emperor Antoku and the imperial regalia. After defeats at Ichi-no-Tani and Yashima, the Taira were annihilated at Dan-no-ura in 1185. While his mother drowned with the child emperor, Munemori jumped into the sea but was pulled out and captured. He was sent to Kamakura and later beheaded at Shinohara in Omi. His failure to drown himself at the end was criticized by posterity.

Gentle but indecisive, he lacked the caliber to lead in wartime. His deep love for his children is shown in the anecdote of his pleading for his son's life before execution.

Depicted as a mediocre commander in "The Tale of the Heike," his sorrowful end is nonetheless retold as a symbol of the Taira's destruction.