The river descends  over its  course and has a catchment area of , which is one of the largest river catchment areas in the Northern Territory. The Roper River is navigable for about , until the tidal limit at Roper Bar, and forms the southern boundary of the region known as Arnhem Land.
The river drops down along its path and has a significant drainage zone, which is one of the biggest in the Northern Territory. The Roper River can be traveled for roughly , until it reaches the tidal point at Roper Bar, and marks the southern boundary of the Arnhem Land area.