The headwaters rise on a plain between the Calvert Hills and China Wall and flow northward through mostly uninhabited lands and pastoral leases such as Calvert Hills Station before finally discharging into the Gulf of Carpentaria 150 kilometres (93 mi) east of Borroloola, not far from the border with Queensland in the Gulf Coastal bioregion.

It has a mean annual outflow of 1,000 gigalitres (1.308×109 cu yd),[2] Before reaching the sea it flows through the Australian Wildlife Conservancy’s Pungalina-Seven Emu Sanctuary.

[4][2] A total of 34 species of fish are found in the river including; the Glassfish, Barred Grunter, Sonub nosed Garfish, Milkfish, Fly-specked Hardyhead, Treadfin Silver Biddy, Flathead Goby, Spangled Perch, Barramundi, Oxeye Herring, Rainbowfish, Black-banded Rainbowfish, Northern Trout Gudgeon, Bony Bream, Catfish, Spotted Scat, Hyrtl's Tandan, Freshwater Longtom, Seven-spot Archerfish and the Giant Gudgeon.

[5] The endangered Gulf snapping turtle has been found in the upper reaches of the river.

He named the river for another member of his party, John Calvert, in acknowledgement of his good service to the expedition.