Nagasaki Unzen has a humid subtropical climate (Köppen Cfa) characterized by warm summers and cool winters with light to no snowfall.

After the Meiji restoration, the villages of Tabira, Doguro, Jindai, Furube, Ifuku, Saigo, Moriyama, Yamada Aino, Chijiwa, Obama, Kuchiyama and Minamikushiyama were established in Minamitakaki District, Nagasaki with the creation of the modern municipalities system on April 1, 1889.

The city of Unzen was established on October 11, 2005, from the merger of the towns of Aino, Azuma, Chijiwa, Kunimi, Minamikushiyama, Mizuho and Obama (all from Minamitakaki District).

[5][6] Unzen has a mayor-council form of government with a directly elected mayor and a unicameral town council of 19 members.

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