From the mouth of Frotet Lake (located north of the lake), this river winds the Jamésie on 451 kilometers to finally reach the Rupert Bay close to the mouth of the Nottaway River.

At the end of the route, the river crosses marsh areas for 29.2 kilometres (18.1 mi) to the west.

The Broadback, together with the Nottaway and Rupert rivers, was initially considered to be dammed and diverted as part of the James Bay Project.

However, in 1972 hydro-electric development began on the more northerly La Grande and Eastmain Rivers, and the NBR Project was shelved.

With the decision to divert the Rupert River to the La Grande, it is not likely that the Broadback will be developed in the foreseeable future.