Joséphine was the eighth of ten children born to Charles Morneault and Pélagie Thériault of Saint-Jacques. She studied at Hôtel-Dieu Academy and Normal School in Fredericton. Later she studied nursing in Nashua, New Hampshire, and graduated in 1922. Ten years later, she became a nun at Hôtel-Dieu in Saint-Basile, and in 1938, with the help of Sister Carroll of Campbellton, she founded a school of nursing for the Sisters. In 1943, some young girls of the region were admitted. Sister Saint-Charles was also a missionary in Peru.