Longlac is located on Long Lake, 320 kilometers east of Thunder Bay, Ontario and adjacent to the native reservation community of "Little Long Lac". It lies approximately halfway between Toronto, Ontario and Winnipeg, Manitoba. Long Lake was inhabited by the Ojibwa prior to European contact. In the 17th century the site became part of the fur trading route used by voyageurs, and later the Hudson's Bay Company and the North West Company.
In 1914 the Canadian Northern Railway was built through Longlac, as part of the Lake Superior route from Port Arthur to Hornepayne and eastern Canada. The Canadian Northern was absorbed by Canadian National Railways in 1918. Following the 1924 completion of Canadian National's Longlac-Nakina Cut-Off, connecting the tracks of the Canadian Northern at Longlac with the former National Transcontinental Railway at Nakina, eastern Canadian rail traffic to or from Winnipeg and beyond, was routed over the rails of the NTR west of Nakina. This is the route through Longlac used by the Canadian National Railway today.
Longlac was connected to Highway 11 in 1942.