He took part in the planning of the Taihō Code alongside Prince Osakabe and Fujiwara no Fuhito, and in 701 was promoted to head of the Ministry of Popular Affairs.

Mahito was also appointed as chief diplomat on a mission to Tang China, receiving a ceremonial sword settō (節刀) from Emperor Tenmu as a symbol of his command.

In mid-702 he was promoted to sangi, and a month later departed for China, accompanied by Yamanoue no Okura and the monk Dōji (道慈) and bearing the Taihō Code.

In addition to restoring normal relations, the mission also allowed for the continued maintenance of Ritsuryō, and offered an opportunity to inform China of Japan's name change from Yamato (倭) to Nihon (日本).

He was promptly promoted to chūnagon to put the knowledge he gained in China to use in the planning of the Keiun Reform [ja] of Ritsuryō.