It is on the middle reaches of the Shimanto River, and faces the Pacific Ocean (Tosa Bay) to the east, and borders Ehime Prefecture across the Shikoku Mountains to the northwest.

During the Edo period, the area was part of the holdings of Tosa Domain ruled by the Yamauchi clan from their seat at Kōchi Castle.

Following the Meiji restoration, the village of Kubokawa was established within Takaoka District, Kōchi with the creation of the modern municipalities system on October 1, 1889 and was raised to town status on February 11, 1926.

Shimanto has a mayor-council form of government with a directly elected mayor and a unicameral town council of 18 members.

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