Son of a reputed poet, he graduated in the Kanto Institute. During his convalescence from a traffic accident he began to write. Two of his first novels obtained a prize in 1961 and very soon he attracted the attention of a Toho film company, which adapted one of his novels in 1963. Although his speciality is mystery novels, he is better known for his historical and chanbara creations: "10 Brave Knights of Sanada", the new version of "Musashi Miyamoto" and above all "Monjiro Kogarashi". "Kogarashi (Cold Wind) Monjiro" was first made into a popular TV Series in 1972-73 directed by Kon Ichikawa and starring Atsuo Nakamura as Monjiro. Its success was so great that Toei made two films this same year based on the story, but with a different team: Sadao Nakajima directing and Bunta Sugawara playing Monjiro. Nakamura played Monjiro in a second TV Series in 1977-78 and finally in the film "The Return of Monjiro Kogarashi" ("Kaette Kita Kogarashi Monjiro", 1993), the last adaptation of a Sasazawa original. Sasazawa himself played bit parts in some movies.