Long before the construction of this church, Innu families from Nitassinan and other First Nations visited the region known today as Tadoussac. The Innu lived in small family groups over a vast territory, moving from one camp site to another and travelling long distances to hunt many species of game and to fish. Families would gather periodically to take part in group hunts or to participate in large summer gatherings in order to engage in trade and enter into matrimonial agreements, among other things. These annual gatherings also allowed for various trade items to be sent to Tadoussac, which is strategically located at the confluence of the Saguenay and St. Lawrence Rivers. Long before meeting the French, the Innu traded with various fishermen and European traders, including Basques, who hunted whales in the Gulf and estuary of the St. Lawrence.
In 1642, the Jesuits established the Sainte-Croix mission, which became the base of their missionary efforts. A decade later, the French established a trading post there. Carpenter Michel Lavoie built the Sainte-Croix-de-Tadoussac Mission Church at the behest of Father Coquart, between 1747 and 1750, with financial and material support from intendants Gilles Hocquart and François Bigot. Its features and construction methods make it an exceptional example of the mission churches of New France and of wooden churches built in Quebec and Canada. Constructed at a time when Tadoussac was an active centre in the fur trade, the church bears witness to the relationship between the fur trade, the missionary efforts of the Jesuits, and First Nations. The Oblate Missionaries of Mary Immaculate established themselves at this mission post in the mid-19th century, continuing to serve the religious needs of the Indigenous population.
The church is rectangular in shape with a front-gable roof and a small bell tower. A sacristy was added to the rear of the church in 1853. The original wood siding, consisting of vertical planks, was replaced in 1866-67 with horizontal clapboard siding, which remains a distinctive external feature. Inside the church, there is a rectangular nave with a central aisle and a choir loft enclosed by a railing. A small gallery occupies the back of the nave. The principal decoration in the choir loft is a tomb-shaped altar dating from sometime between 1790 and 1840, surmounted by a tabernacle painted white with gold leaf highlights, which was added in 1790. The church is oriented towards Tadoussac Bay and the St. Lawrence River, in order to welcome the Innu and missionaries who were carried by the waterways when then came to Tadoussac. The church has undergone various changes over time, but maintains a high level of its original character.