A warrior of the Miura clan, grandson of Miura Yoshiaki and son of Sugimoto Yoshimune. From the very start of Minamoto no Yoritomo's uprising in 1180 he served the cause, distinguishing himself in numerous battles. When the Kamakura shogunate was founded he was appointed the first head of the Samurai-dokoro, the board governing the gokenin (vassals) and overseeing military and police affairs. Renowned as a master archer, he was one of Yoritomo's most trusted senior advisers. After Yoritomo's death he joined the council of thirteen, but as the Hojo rose to power their rivalry deepened. In 1213 he raised arms against Hojo Yoshitoki in what became the Wada Rebellion. After fierce fighting in the streets of Kamakura he was defeated, and he and his clan were destroyed. He was 67. The Wada-zuka mound in Kamakura preserves the memory of his end.

Famed for his valor and skill with the bow, Yoshimori commanded the respect of the warrior class as a senior adviser from Yoritomo's day. Warm-hearted and devoted to his clan, he was nonetheless outmaneuvered by the political cunning of the Hojo, and in the end staked his clan's honor on a doomed uprising.

As the first head of the Samurai-dokoro, Yoshimori helped lay the military foundations of warrior government. The destruction of his clan in the Wada Rebellion is remembered as a symbolic step in the Hojo consolidation of power over the shogunate. The Wada-zuka in Kamakura still tells of the clan's end.