Narita Nagayasu served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was the lord of Oshi Castle in Musashi Province.

The Narita clan descended from Fujiwara no Morosuke, a noble from the early to middle Heian period.  The Narita worked as servants of the Yamanouchi-Uesugi family for generations.

Around 1495, Nagayasu was born as the son of Narita Chikayasu.  Initially, he served Uesugi Norimasa, the deputy shōgun of the Kantō.

In the fourth month of 1545, after the death of his father, Chikayasu, Nagayasu inherited the headship of the clan.  Owing to an ongoing struggle with the Gohōjō, the Yamanouchi-Uesugi declined so, in the fifth month, Nagayasu submitted to the Gohōjō clan.  In 1560, Nagao Kagetora (later Uesugi Kenshin) of Echigo Province led an army of approximately 100,000 men to invade the Kantō whereupon Nagayasu came under his command.  The Uesugi army proceeded to lay siege to the main base of the Gohōjō at Odawara Castle in Sagami Province in an event known as the Siege of Odawara Castle.  After Kagetora returned to Echigo, Nagayasu surrendered to Hōjō Ujiyasu and became a retainer.

According to one account, in Kamakura, during the ceremony for Kenshin to become the deputy shōgun of the Kantō, some of the bushō bowed down to pay their respects.  Nagayasu, having come from a prominent family descended from the Fujiwara clan, paid his respects from atop his horse.  Unaware that this was his custom, Kenshin regarded the act as disrespectful and thrashed Nagayasu in the face with his folding fan.  After the encounter, Nagayasu withdrew his soldiers to his base.  Later, this incident is said to have been a catalyst for other bushō in the Kantō to revolt, but this thrashing of Nagayasu is not recognized as fact among scholars.  He is said to have come into conflict with Kenshin in regard to the return of the Hanyū territory in Musashi.

In 1563, after an attack by Kenshin at Oshi Castle, Nagayasu surrendered.  As a result, he was ordered to retire and transfer headship of the clan to his lineal heir, Narita Ujinaga.  In 1566, however, he attempted to remove Ujinaga and install his second son, Narita Nagatada (Yasuchika) as the head of the clan.  This led to a conflict with Ujinaga as well as opposition from his younger brother, Narita Yasusue, and a veteran named Toshima Mino-no-kami, so he abandoned the plan, entered the priesthood, and retired.

In 1574, Nagayasu died at the age of seventy-nine.