Sagae Munehiro served as a bushō during the Sengoku period.  Munehiro was the fourteenth head of the Sagae clan and seventh lord of Sagae Castle in the Sagae manor in the Murayama District of Dewa Province.

Munehiro was born as the eldest son of Sagae Tomohiro, a bushō, the thirteenth head of the Sagae clan and sixth lord of Sagae Castle.  In 1494, upon the death of his father, Munehiro inherited the Sagae clan.  That same year, Mogami Mitsuuji, a sengoku daimyō in Dewa, died and was succeeded by Mogami Yoshiatsu. Meanwhile, owing to conflict in his territory, Date Hisamune fled for the protection of the Ashina clan.

Tomohiro moved to Sagae the Ryōin-Chōkōin sub-temple of the Chōshū-Tainei Temple built to worship his two parents and called it the Zuiryūsan-Chōkō Temple.  He received a consort from the Yamanobe clan and had his daughters wed members of the Yamanobe and Nakano clans to forge relationships through marriage with these clans.  In addition, his sister wed Nakano Yoshitatsu.

Mogami Yoshiatsu, the Oushū-tandai, or local commissioner of Oushū, who became the head of the Mogami around the same time, received the title of Assistant Captain of Outer Palace Guards of the Left Division (equivalent to Junior Fifth Rank (Upper)).  By comparison, Munehiro adopted the title of Master of the Eastern Capital Office (equivalent to Junior Fourth Rank (Lower).

Following his death on 7/1 of Eishō 1 (1504), Munehiro’s son, Sagae Takahiro, was still in his youth so a succession struggle erupted in the family.  That same year, Mogami Yoshiatsu also died, triggering an invasion by his successor, Mogami Yoshisada.