Saitō Toshishige served as a bushō during the late Muromachi and Sengoku periods.
Toshishige was born as the son of either Saitō Myōjun or Saitō Toshitame. His common name was Taitō-zaemon-no-jō. There is a theory that he was the same individual as Saitō Matashirō. Toshishige had a son named Bisha-tokumaru.
From around 1521, he replaced Saitō Toshiyoshi as the deputy military governor serving under Toki Yoritake, the military governor of Mino Province. According to records from the Funyō Temple, in this same year, he issued a prohibition against the Funyō Temple. In 1525, Nagai Nagahiro and Nagai Shinzaemon launched a rebellion against Yoritake, pledging support for Yoritake’s younger brother, Toki Yoriaki. The rebel forces occupied the Fukumitsu residence of the military governor and attacked Inabayama Castle where Toshishige resided. In 1530, after Yoritake fled for the protection of the Asakura clan in Echizen Province, the Nagai clan, an illegitimate branch of the Saitō, held the real power in Mino.
Thereafter, continuing opposition to the faction supporting Yoriaki led to conflicts with Nagai Norihide (later known as Saitō Dōsan) who inherited the surname of the Nagai clan. In the seventh month of 1536, after Yoriaki became the military governor of Mino, Toshishige abandoned the son of Yoritake, Toki Yorizumi, and, through the mediation of Rokkaku Sadayori, switched his allegiance to Yoriaki. In 1538, based on documents from the Agan Temple, the rights of the temple to their landholdings were officially recognized. His movements can be ascertained until 1541, but, when Yoriaki was expelled by Dōsan, Toshishige is said to also have been ousted and fell into ruin.