Mary's Harbour is located on the Southern Labrador coast at the mouth of St. Lewis Inlet. Although the community dates back only to the 1930's, St. Mary's River was the site of a salmon fishery from the 1780's.

After a fire at Battle Harbour in 1930, the International Grenfell Association decided to relocate its hospital and boarding school from Battle Harbour to Mary's Harbour. The first permanent resident in thought to be Samuel Acreman, who supervised construction of the Grenfell Mission. By 1935 there were 18 people living at Mary's Harbour year-round. Today the population is 417.