The Namoi River is a river in inland New South Wales, Australia.

The headwaters of the Namoi, including the Macdonald River, the Peel River, the Cockburn River and the Manilla River, rise on the western slopes of the Great Dividing Range in northern New South Wales. Flowing generally westward, they join to form the Namoi River near Gunnedah in the Liverpool Plains. The Namoi then flows westwards past Narrabri and Wee Waa and eventually joins the Barwon River, near the town of Walgett.

Keepit Dam near Gunnedah is an important dam for flood control and irrigation. The floodplains of the lower Namoi around Wee Waa are an important area for growing cotton which is irrigated using water from the dam.