Minamiuonuma is situated in a valley in a mountainous region of Niigata Prefecture, located on Honshu, Japan's largest and most centralised island.

Dotted with ski lodges and other winter activity facilities, the city is in a region known as "Snow Country"; indeed, Minamiuonuma sits at an average elevation of around 617 m (2,024 ft) above sea level,[3] creating a wintry climate in the coldest months of the year.

The city and its surrounding areas are dotted with many onsen (hot springs) and ski resorts, making it a popular destination in winter.

Minamiuonuma has a Humid climate (Köppen Cfa), characterised by warm, wet summers and cold winters, with heavy snowfall.

The village of Muikamachi was created with the establishment of the modern municipalities system on April 1, 1889, and was elevated to "town" status on July 13, 1900.