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 flows downhill over its route and encompasses a substantial watershed area, which is among the largest in Northern Territory. The Roper River is passable for around , until it reaches the tidal boundary at Roper Bar, and forms the southern edge of the Arnhem Land territory.