Eugene renounced his family's wealth, and preferred to become a parish priest in Aix-en-Provence, working among the poor, preaching missions and bringing them the church in their native Provencal dialect, not the French used by the upper classes.
Eugene realized the need for formal organization, and on 17 February 1826 he received approval from Pope Leo XII to found a new congregation, the Oblates of Mary Immaculate founded on his core of missionaries.
Eugene realigned parishes and maneuvered behind the scenes to weaken the government monopoly on education.
DeMazenod was the offspring of a noble family of southern France, and even in his tender years he showed unmistakable evidence of a pious disposition and a high and independent spirit.
After having aided for some time his uncle, the aged Bishop of Marseilles, in the administration of his diocese, Father DeMazenod was called to Rome and, on 14 October, 1832, consecrated titular Bishop of Icosium, which title he had, in the beginning of 1837, to exchange for that of Bioshop of Marseilles.
DeMazenod unceasingly strove to uphold the rights of the Holy See, somewhat obscured in France by the pretensions of the Gallican Church.