He was a diplomat during the reign of Empress Genshō. And he was minister during the reign of Emperor Shōmu. In the Imperial court, Umakai was the chief of protocol (Shikibu-kyō).
724 (Jinki 1, 1st month): Umakai led an army against the emishi.
But this military campaign was later judged to have been unsuccessful. 729 (Tenpyō 1): The emperor invested Umakai with the power to raise an army to quash a revolt, but the cause for alarm was dissipated without the need for military action.
737 (Tenpyō 9): Umakai died at age 44. Umakai had three brothers: Muchimaro, Fusasaki, and Maro.
These four brothers are known for having established the "four houses" of the Fujiwara.
Umakai"s children included: Fujiwara no Hirotsugu and Fujiwara no Momokawa.
This member of the Fujiwara clan was son of Fujiwara no Fuhito.