was a Japanese statesman and waka poet in the Nara period. He was one of the Man'yō no Go-taika, the five great poets of his time, The Ōtomo clan were warriors and bureaucrats in the Yamato Court, and Yakamochi served as a in several provinces. He was the nephew of Ōtomo no Sakanoue no Iratsume, who was also poet and a favorite of Prince Hozumi. Yakamochi became the head of the Ōtomo family.
In 738, he met Udoneri, and in 740 at the behest of Emperor Shōmu went to Dazaifu (Kyūshū) to suppress the rebellion of Fujiwara no Hirotsugu. In 745 he achieved the rank of in the Imperial court. In July of the following year, he became governor of Etchū Province, a post he lasted in until 751. By this time he was already the author of 220 waka. In 751, he was promoted to and returned to the capital.
In 754, he was appointed , and the following year concerned himself with the at Nanba, a time that is described in the Sakimori Songs Collection in the Man'yōshū. Yakamochi did not take part in the . Instead, he conspired with Fujiwara no Yoshitsugu, Isonokami Yakatsugu and Saeki no Imaemishi to plot the assassination of Fujiwara no Nakamaro. Afterwards Yoshitsugu took sole responsibility for the affair, but due to suspicions about Yakamochi's involvement he was transferred to the governorship of Satsuma Province.
In 777, he rose to the governorship of Ise Province. According to the records of the , he served in this post for about five years. In 780 he was promoted to . Fearing suspicion and banishment from the capital for aiding in Hikami no Kawatsugu's , he remained quiet and was promoted to in 783.
He died in 785 (or the final compiler It also formed part of the Japanese military appropriation of high culture for the historical justification of its existence.