He was the son of Fujiwara no Maro, and, according to the genealogy book Sonpi Bunmyaku, his mother was Uneme of Yakami no Kōri, Inaba Province, who is probably the same person who had a famous affair with Aki no Ōkimi.
Under Empress Kōken, he held high-level positions in various ministries, but his promotion stagnated at this rank until Fujiwara no Nakamaro's rebellion in 764.
He supported Empress Kōken's side in the conflict, and was promoted to ju shi-i no ge (従四位下) a month later.
He held a position as director of the gyōbu-shō, and in 772 was promoted to ju shi-i no jō (従四位上) and sangi, joining the ranks of the kugyō.
In 773, Emperor Kōnin's heir Crown Prince Osabe (他戸親王) was disinherited, and according to the rekishi monogatari Mizukagami, Hamanari opposed Fujiwara no Momokawa's candidate Prince Yamabe, the future Emperor Kanmu, in favor of his brother by another mother, on the grounds that Yamabe's mother was descended from immigrants from Baekje.