Karimganj is situated in the southernmost part of Assam, occupying a prominent position within the Barak Valley. The city lies on the northern bank of the Kushiyara River, which delineates the international border with the Sylhet Division of Bangladesh. To the south, the district borders the state of Tripura, while Mizoram lies to its southeast.
The physical geography of the area is characterized by vast, fertile alluvial plains intersected by a network of rivers and streams, part of the larger Surma-Meghna river system. The rich, loamy soils of the river basin make the region exceptionally suitable for agriculture. While the city itself is primarily a flat riverine plain, the broader district is fringed by lush green hills and extensive forest cover, contributing to a highly biodiverse ecosystem.
Due to its location in a river valley with relatively low elevation, Karimganj is prone to annual flooding during the intense monsoon season, which shapes both the natural environment and the agricultural cycles of the region.