Prior to this, the Finlay joined with the Parsnip River to form the Peace.

The headwaters of the Finlay at Thutade Lake are considered the ultimate source of the Mackenzie River.

The Finlay drains an area of 43,000 square kilometres and discharges at a mean rate of 600 cubic metres per second.

The first European to journey its length to its source was the fur trader and explorer Samuel Black in 1824.

The river was the eastern half of the northern boundary of the Colony of British Columbia at the time of its creation in 1858, north of which was the North-Western Territory; the western half of the boundary was the Nass River and from 1862 to 1863 it was briefly the southern boundary of the Stickeen Territories (Stikine Territory) which had been formed from the North-Western Territory in response to the Peace and Stikine Gold Rushes and which was amalgamated with the Colony of British Columbia in the following year.