Ōmihachiman is located in central Shiga Prefecture, on flatlands along the eastern shore of Lake Biwa, and extending inland to the foothills of the Suzuka Mountains.

Shiga Prefecture Ōmihachiman has a Humid subtropical climate (Köppen Cfa) characterized by warm summers and cool winters with light to no snowfall.

In 1905, an American architect William Merrell Vories came to Ōmihachiman as an English language teacher at commercial high school.

On March 31, 1954, Hachiman merged with the villages of Okayama, Kanada, Kirihara and Mabuchi to form the city of Ōmihachiman.

In terms of national politics, the city is part of Shiga 2nd district of the lower house of the Diet of Japan, and is represented by Kenichiro Ueno.