In addition to Les Méchins (formerly known as Grands-Méchins) itself, the municipality also includes the communities of Anse-des-Méchins, Cherbourg, Cherbourg-Centre, Les Îlets Méchins, and Petits-Méchins.
The name Méchins is of uncertain origin although according to one theory, it may come from the French word méchants, meaning "wicked", and referring to rocks in the sea that would make navigation there dangerous. Another, less likely suggestion is that it may be a transformation of "Matsi", a 2.5 metres (8 ft 2 in) tall one-eyed monster of Mi'kmaq folklore who would come down from the mountains with a stick as big as a tree to terrorize the local people.
Colonization began in 1859 when three families arrived. By 1865, it had grown to 119 inhabitants. The Mission of Saint-Édouard was established in 1876 and the following year, the area was incorporated as the United Township Municipality of Dalibaire-et-Romieu. In 1880, the chapel was completed and its registers were opened. From that year onward, the place experienced a development boom due to the founding of a herring smokehouse and maritime industry, including ship building in the late 19th century.
While Méchins became a separate municipality in 1952, it was not until 1982 that the current Municipality of Méchins was formed through the merger of Méchins with Saint-Paulin-Dalibaire (formed in 1954) and Saint-Thomas-de-Cherbourg (formed in 1954).