Archaeological digs found that the Amerindians had been in the region for over 12,000 years, making this the oldest known site of human occupation in Quebec.

Nearby Agnès, founded in 1895, was named after Susan Agnes Bernard, the widow of Prime Minister of Canada Sir John A. Macdonald.

An important figure of Lac-Mégantic was Joseph Édouard Eugène Choquette, a priest, who, in his spare time, was an amateur scientist.

He was the catalyst for the creation of an electric lighting system which, on the eve of Christmas in 1898, illuminated the entire city; and a power company.

Morrison's family had immigrated from the Isle of Lewis, in the Outer Hebrides of Scotland and had settled locally in a largely Canadian Gaelic-speaking farming community.

[6] Donald Morrison moved out west to work as a cowboy on a ranch, sending money home to pay off the family debts.

When he returned home, he found his family had lost their farm after they had signed a bad debt deal with Mayor MacAuley, the wealthiest resident in the town at the time.

[6] At approximately 01:15 EDT,[8][9] on July 6, 2013, an unattended 73-car[10][11][12] freight train carrying crude oil ran away and derailed near the downtown area of Lac-Mégantic, causing multiple tank cars to catch fire and explode.

Although the railway has declined in recent decades, Lac-Mégantic remains an important centre of agriculture, logging, lumber and pulp and paper.

Sonae Indústria's local subsidiary, Tafisa Canada, operates a 65,000 square feet (6,000 m2) particleboard factory in the town.

[6][24][25] Other major local employers include furniture manufacturer Bestar[26] and forestry company Industries Manufacturières Mégantic,[27] part of Masonite International.

The region's economy in its early days was propelled by the logging industry due to the vast swaths of old-growth forests.

[34] A weekly newspaper, L'Écho de Frontenac, is published in the town[35] and one radio station, CJIT-FM 106.7, operates from a local studio.

The region has increased its reliance on tourism, a mainstay since the passenger rail era, attracting people from across Quebec and the Northeastern United States.

Lac Mégantic is home to a junior college, Centre d’études collégiales de Lac-Mégantic, which is affiliated with the Cégep Beauce-Appalaches.

[39] As the original collection was destroyed by fire in 2013, a hundred thousand books were donated by local groups, universities, authors and publishers across Québec.

After that company's 2003 bankruptcy, the Montreal, Maine and Atlantic Railway provided freight service until the line in both directions was severed by the Lac-Mégantic derailment in 2013.

MM&A claimed bankruptcy protection in August 2013; its assets were sold to Fortress Investment Group as the Central Maine and Quebec Railway in 2014.

[42] Lac-Mégantic is home to the Centre de santé et service sociaux (CSSS) du Granit, which is located on Laval Street.