After the Meiji Restoration, the establishment of the modern municipalities system created Minamiashigara, Fukusawa, Okamoto and Kitaashigara villages within Ashigarakami District, Kanagawa Prefecture.

Minamiashigara was elevated in status to that of a town on April 1, 1940, and annexed neighboring Fukusawa, Okamoto and Kitaashigara villages in 1955.

Minamiashigara has a mayor-council form of government with a directly elected mayor and a unicameral city council of 16 members.

Minamiashigara, collectively with the municipalities of Ashigarakami District, contributes one member to the Kanagawa Prefectural Assembly.

In terms of national politics, the city is part of Kanagawa 17th district of the lower house of the Diet of Japan.