The mainstream of the river system flows for . The river's headwaters arise from the wet heath and bog at the foot of Peppercorn Hill situated along Long Plain which is within the Fiery Range of the Snowy Mountains; and about north of Kiandra. From its headwaters it flows to its confluence with the Murray River. The river flows for through the Australian Capital Territory near Canberra, picking up the important tributaries of the Gudgenby, Queanbeyan, Molonglo and Cotter Rivers. The Murrumbidgee drains much of southern New South Wales and all of the Australian Capital Territory, and is an important source of irrigation water for the Riverina farming area.