Suganuma Sadatsugu served as a bushō during the Sengoku period.  He was the fourth head of the Damine-Suganuma clan and lord of Damine Castle in the Kitashitara District of Mikawa Province.

Sadatsugu was born as the eldest son of Suganuma Sadahiro.  Sadatsugu was the nephew of Suganuma Sadanori, the first head of the Noda-Suganuma clan.

The timing when he inherited the headship of the clan from Sadahiro is uncertain.

In 1532, he built Shin Castle (Shinjō) in Sato-ga-hara in the Shitara District.  His former base at Ōtani Castle was called Hon Castle so Shin Castle embodied the meaning of a new castle.  This was different from Shin Castle (Shinshiro) built later by Okudaira Nobumasa.

In 1556, after Okudaira Kenmotsu Sadakatsu, the lord of Kameyama Castle, defected from the Imagawa clan, owing to the remarriage of his younger sister, Sadatsugu supported Sadakatsu.

After the Okudaira and Suganuma clans joined forces in opposition to the Imagawa, the Okudaira led uprisings in two locations in the Nukata District and the Suganuma rose up in the Shitara District of Mikawa.

On 2/15 of Kōji 2 (1556), the Okudaira clan holed-up and took over Hadanashi Castle in the Nukata District.  Further, at Hijika, the Okudaira repelled Imagawa forces led by Tōjō-Matsudaira Tadashige dispatched to suppress them yielding a promising victory.  This is known as the Battle of Hijika.

Sadatsugu’s younger brothers, namely, Sadanao, Sadauji, and 定仙, opposed him, choosing instead to remain on the side of the Imagawa.  Moreover, among the branch families of the Suganuma, those aligning with Sadatsugu were limited to Suganuma 定圓 and Suganuma Sadayori (the younger brothers of Suganuma Sadamura who was the son of Sadatsugu’s uncle, Suganuma Sadanori) along with Magodayū from the Shimada-Suganuma family.  None of the families supported Sadatsugu en masse, causing a loss of standing for the main branch of the family.  In the fifth month of the same year, he clashed with his younger brothers and routed them at the Battle of Furi.

After receiving orders from Imagawa Yoshimoto in Sunpu to actively engage in suppression activities, bushō from eastern Mikawa invaded Ameyama in the Nukata District which was held by the Achiha clan who were relatives of and aligned with the Okudaira.  On 8/4, the supporters of the Imagawa prevailed at the Battle of Ameyama.  This resulted in the surrender of Okudaira Sadakatsu, the brother-in-law of Sadatsugu – the ringleader of the rebellion against the Imagawa.

On 8/21, Sadatsugu, standing with an isolated army, was subject to a counterattack by the suppression army comprised of members of the branch families of the Suganuma.  Facing defeat, Sadatsugu and his supporters scattered in all directions with his opponents sternly in pursuit.  Perhaps realizing that he could not reach Damine Castle, Sadatsugu and a small group with him took their lives at Kuronuta in Furi.  Under another theory, he was killed in action or murdered.

Members of the Suganuma clan siding with the Imagawa continued an offensive toward Damine Castle, occupying the site.  The rebellion came to an end.  At this time, there was a lineal heir of Sadatsugu named Kobōshi (later known as Suganuma Sadatada) protected by the suppression army outside of Damine Castle.  Sadatsugu’s younger brothers welcomed Kobōshi as the successor to Sadatsugu and continued to loyally serve on behalf of the Imagawa clan.

The place called Kuronuta in Furi is forgotten and the location unknown.