Sassa Nagaaki served as a bushō from the Sengoku to early Edo periods. He was a retainer of the Oda clan of Owari Province.
Nagaaki was born as the son of Sassa Yoshinori, a retainer of the Oda clan. Initially, he served the Oda clan, following his father who was responsible for negotiations with the Echigo-Uesugi clan. He was active diplomacy with the Uesugi clan uring the Eiroku era (1558 to 1570). In 1575, Nagaaki participated in the conquest of the Echizen ikkō-ikki. He then served as a yoriki, or security official, for Yanada Hiromasa and became the chamberlain for Hinoya Castle in Kaga Province. He worked tirelessly to pacify the uprisings, but struggled to make progress and, after Hiromasa was discharged from his position, Nagaaki also returned home.
In 1578, after the sudden demise of Uesugi Kenshin, Nagaaki was sent to Etchū Province with reinforcements for Jinbō Nagazumi to fight against the Uesugi army. After the coup d’état against Oda Nobunaga in the sixth month of 1582, Nagaaki served Oda Nobukatsu (Nobunaga’s second son) and received landholdings with a value of 350 kanmon in the Aoyama township of Owari. Later, he served Toyotomi Hideyoshi as an umamawari, or cavalry soldier. In the 1590’s, during the Bunroku-Keichō Campaign on the Korean Peninsula, he was assigned to Nagoya Castle in Hizen Province in support of the expeditions.
According to genealogical records, Nagaaki is identified as the younger brother of Sassa Narimasa but there are questions in this regard. According to the same records, he was killed in action during the Summer Campaign of the Siege of Ōsaka in 1615.