Born the eldest son of Taira no Kiyomori, Shigemori lived through the zenith of the Taira clan's prosperity. He fought under his father in the Hogen Rebellion (1156) and Heiji Rebellion (1159), contributing to the rise of the Taira. Graceful in appearance and outstanding in virtue, he was known within the Taira clan as a moderate. When his father Kiyomori took a hard line toward Retired Emperor Go-Shirakawa, tradition holds that Shigemori remonstrated against the excess. He rose to the posts of Minister of the Interior and Commander of the Left Imperial Guards and was eagerly awaited as the Taira heir, but died of illness in 1179 at the young age of 42. It is said that after Shigemori's death Kiyomori's arbitrary behaviour intensified and his confrontation with Go-Shirakawa became irreparable. In the Tale of the Heike he is depicted as a loyal subject who grieved over his father's tyranny yet strove to uphold the duty of lord and subject, with his tragic quality emphasised. Some assessments hold that his sudden death removed the last brake on the Taira clan's path to destruction.

In contrast to his father Kiyomori's fierce temperament, he is said to have been gentle and to have placed great importance on moral principle — a moderate by nature. In the Tale of the Heike he is depicted as an embodiment of Confucian virtues such as benevolence, righteousness, propriety, wisdom and trustworthiness, said to have spent his life grieving the path that led to the Taira destruction. He died young, and his potential was never fully realised.

As the symbol of the morally upright Taira warrior in the Tale of the Heike, he exerted great influence on later literature and art. The historical assessment holds that while Shigemori was restraining Kiyomori's excesses the Taira enjoyed relative stability, and that his early death accelerated the clan's destruction. Jakkoin temple in Ohara, Kyoto, is said to have connections with Shigemori.