Nagai Hidehiro served as a bushō during the Sengoku period. His common name was Shichirōemon-no-jō. He held the title of Governor of Etchū. His son was Nagai Nagahiro.
Nagai Hidehiro first appears in records from the eleventh month of 1462 kept by the Zenne Temple in the Kamo District of Mino Province.
Saitō Myōchin, the founder of the Jizein branch of the Saitō family, resided in the Zenne Temple until 1460. Following the death of Myōchin in the second month of 1480, Hidehiro served Saitō Myōjun who succeeded Myōchin as the head of the Jizein branch. In 1495, Ishimaru Toshimitsu initiated the Battle of Funada, backing Saitō Toshiharu (the grandson of Saitō Toshifuji, the deputy military governor) against Toki Motoyori (the youngest son of Toki Shigeyori, the military governor of Mino).
During this battle, Hidehiro defended Saitō Myōjun of Kanō Castle, killing Ishimaru Toshisada, a commanding general, and sent his opponents fleeing in defeat.
On 12/7 of Meiō 5 (1497), however, while returning to Mino from an expedition to subdue Rokkaku Takayori in southern Ōmi Province, Hidehiro was swept-up in a local uprising and, along with his lord, Saitō Myōjun, was killed in action.