Archeological digs have revealed that the island was occupied by Amerindian groups at least 2,000 years ago. But the first written reference that has been found seems to date back to Samuel de Champlain in 1603; he provided a brief description without naming it officially. It was named Île Saint-Paul in honour of Paul de Chomedey, Sieur de Maisonneuve, who co-founded Montréal with Jeanne Mance.
Owned by Jean de Lauson in 1634, the island was ceded to three people, in equal shares, in 1664. The north-east was transferred to Jacques Le Ber, the centre to Claude Robutel de Saint-André, Sieur de Lanoue, and the south-west went to Jean-Baptiste Lavigne. In 1668, the latter transferred his portion of the island to Marie Le Ber, who gave it to her brother Jacques. The two portions held by Le Ber were known as the Fief Saint-Paul and the centre was identified as the Fief Lanoue. In 1668, the population of the island was 20 souls.
In 1706, the nuns of the Congrégation de Notre-Dame purchased part of the Fief Lanoue and Jeanne Le Ber, Jacques’ daughter, gave them a certain number of acres from the Fief Saint-Paul. In 1769, the nuns became the sole owners of the island. For a long time, no nuns lived on a permanent basis on the island. They did, however, erect a stone house there in 1788 and cultivated approximately one-third of the area of the island. In addition to its agricultural function, the island also served as a place of rest and relaxation for the nuns of the Congrégation de Notre-Dame.