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.

[5] The town of Hachiman was established with Gamō District, Shiga with the creation of the modern municipalities system on April 1, 1889.

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

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.