Suganuma Sadanao served as a bushō during the Sengoku period.  Sadanao was the younger brother of Suganuma Sadatsugu, the fourth head of the Damine-Suganuma who were a member of the kunishū, or provincial landowners, in Mikawa Province.

A majority of the kunishū in Mikawa, including the Damine-Suganuma, submitted to the Suruga-Imagawa clan following their invasion of the province in the early Sengoku period.  In 1555, early signs of internal conflicts and rebellions occurred primarily in eastern Mikawa in an event known as the Furious Drama of Mikawa.  Suganuma Sadatsugu, the head of the Damine-Suganuma, opposed the Imagawa clan.  Nevertheless, Sadatsugu’s three younger brothers, namely, Sadanao, Sadauji, and 定仙, in addition to an official named Hayashi Ukyō-no-jō, sided with the Imagawa and attacked Sadatsugu, resulting in his demise.  After the battle, Sadanao and others backed Sadatsugu’s son, Kobōshi (later known as Suganuma Sadatada) as the successor of Sadatsugu which was authorized by Imagawa Yoshimoto.

In 1561, after Matsudaira Ieyasu (later known as Tokugawa Ieyasu) defected from the Imagawa clan, in a letter dated 4/15 from Ieyasu to Sadanao and the Damine-Suganuma clan, he promised “official recognition of the rights of Suganuma Sadatada to his territory, the freedom of movement of members of the clan, the allocation of landholdings in Tōtōmi, and the freedom of movement of Shitara Sadamichi.”  Sadanao is indicated as the leader among those to whom the sealed document is addressed.  Together with other members of the family, Sadanao supported their youthful lord, Sadatada, and participated in managing the affairs of the Damine-Suganuma clan.

In the first month of the next year, the Damine-Suganuma clan, through the mediation of Okudaira Sadayoshi, re-engaged in service to the Imagawa clan.  Later, after Ieyasu achieved the unification of Mikawa, the Damine-Suganuma served the Matsudaira clan.

Thereafter, Sadanao’s movements are unknown.  In the tenth month of 1572, after Takeda Shingen commenced the invasion of Mikawa and Tōtōmi, the Damine-Suganuma clan split with Sadatada and 定仙 supporting the Takeda and Sadauji and others aligning with the Tokugawa.  At this time, Sadanao’s name cannot be confirmed from records so he is surmised to have died by then.

Suganuma Sadatoshi, who governed the Ina District of Shinano Province under the Tokugawa clan, is deemed the son of Sadanao.