After the death of his father Tadamori in 1153, Kiyomori assumed control of the Taira clan and ambitiously entered the political realm in which he had previously only held a minor post. In 1156, he and Minamoto no Yoshitomo, head of the Minamoto clan, suppressed the Hogen Rebellion. This established the Taira and Minamoto samurai clans as the top political powers in Kyoto. However, their new strength in effect caused the allies to become bitter rivals which culminated three years later in the Heiji Rebellion in 1159. Kiyomori, emerging victorious with Yoshitomo and his two eldest killed, now remained the greatest political power in Kyoto. Kiyomori then exiled Yoshitomo's three youngest sons Yoritomo, Noriyori, and Yoshitsune and seized most of the manors of his rivals.
As the greatest political power and owner of the majority of manors in the Japan, he amassed unrivaled wealth and power. In 1167, Kiyomori was the first samurai to be appointed Daijyo Daijin, chief minister of the government, the de facto administrator of the imperial government. Though he relinquished the position later in the year and relinquished the leadership of the clan, he remained the orchestrator of the government policy and successfuly placed his family members and allies in most of the government posts and as magistrates of nearly half of the provinces of Japan.
In 1171, Kiyomori forced the marriage between the emperor Takakura and his daughter Tokuko. Their first son, Prince Tokihito was born in 1178. The next year, in 1179, Kiyomori staged a coup d'etat forcing the resignation of his rivals from all government posts and subsequently banishing them, then filled the open government positions with his allies and relatives, and imprisoning the cloistered emperor Go-Shirakawa. Finally, in 1180 Kiyomori forced the emperor Takakura to abdicate and give Prince Tokuhito the throne, becoming the emperor Antoku.
With the exertion of Taira power and wealth and Kiyomori's new monopoly on authority, many of his allies, most of the provincial samurai, and even members of his own clan turned against him. Prince Mochihito, brother of emperor Takakura, called on Kiyomori's old rivals of the Minamoto clan to rise against the Taira beginning the Genpei War in the middle of 1180. Kiyomori died early in the next year from sickness, leaving his sons with the downfall and destruction of the Taira at the hands of the Minamoto.
Taira no Kiyomori is also the main character in the Kamakura period epic, the Tale of Heike.