Saotome was born in Harbin, China. He attended Keio University's Literature Department, but left school before graduating. In 1954, the noted author, Yamamoto Shugoro, agreed to become his tutor.

In 1956, together with other like-minded authors, he formed a literary criticism group called Shosetsu Kaigi ("Fiction Conference"), with members supporting each other by reviewing each other's work. One of the products of this collaboration was his novel Kyojin no Ori, which was awarded the prestigious Naoki Prize in 1968.

Saotome claimed that his ancestry from a samurai of Aizu-Wakamatsu domain has led to his interest in historical matters, and the bulk of his work has been historical fiction set in the Sengoku, Edo or Bakumatsu periods. Many of his works have been adapted into movies or television series.

In 2006, he was elected the chairman of the Japanese P.E.N.

Saotome, after contracting a stomach cancer, died at a hospital in Kamakura, Kanagawa Prefecture, Japan. His family announced his death to the media.

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