In the early Meiji period, the village of Arasawa was created within Ninohe District on April 1, 1889, with the establishment of the modern municipalities system.

Likewise, on April 1, 1889, the villages of Tairadate, Obun, Dendo and Terada were established within Kita-Iwate District.

The city of Hachimantai was established on September 1, 2005, from the merger of the towns of Ashiro and Nishine, and the village of Matsuo.

Hachimantai has a mayor-council form of government with a directly elected mayor and a unicameral city legislature of 22 members.

In terms of national politics, the city is part of Iwate 2nd district of the lower house of the Diet of Japan.