Paul-Émile Léger was born in Valleyfield on April 26, 1904; the son of Ernest Léger and Alda Beauvais and brother of Jules, who played a leading role in Canadian diplomacy. He did his classical studies at the Seminary of Sainte-Thérèse and his theological studies at the Grand Séminaire de Montréal. He was ordained priest on March 25, 1929, by Msgr. Georges Gauthier, for the diocese of Valleyfield.

As a priest, he enrolled at Saint-Sulpice and left for Paris where he went into his "solitude". He obtained a degree in theology and canon law and taught the latter discipline at the Seminary of Issy-les-Moulineaux (1929-1933).

His first appointment took him on a mission to Japan where, for six years, he was the founding superior of the Fukuoka Seminary (1933-1939). He then returned to Montreal to teach sociology at the Seminary of Philosophy (1939-1940). He then devoted seven years to Valleyfield where he was vicar general of the diocese and parish priest of the cathedral (1940-1947). Finally, he became rector of the Canadian Pontifical College in Rome and was its director for three years (1947-1950).