He came of a rich family which had renounced the Jewish for the Catholic religion. From the same family sprang the better known Frédéric Ozanam. Though he began the study of theology to please his father, he was more strongly attracted to mathematics, which he mastered without the aid of a teacher. At the age of fifteen he produced a mathematical treatise. Upon the death of his father, he gave up theology after four years of study and began, at Lyon, to give free private instruction in mathematics. Later, as the family property passed entirely to his elder brother, he was reluctantly driven to accept fees for his lessons.
In 1670, he published trigonometric and logarithmic tables more accurate than the then existing ones of Ulacq, Pitiscus, and Briggs. An act of kindness in lending money to two strangers secured for him the notice of M. d'Aguesseau, father of the chancellor, and an invitation to settle in Paris. There he enjoyed prosperity and contentment for many years. He married, had a large family, and derived an ample income from teaching mathematics to private pupils, chiefly foreigners.
His mathematical publications were numerous and well received. The manuscript entitled Les six livres de l'Arithmétique de Diophante augmentés et reduits à la spécieuse received the praise of Leibnitz. Récréations, translated later into English and well known today, was published in 1694. He was elected member of the Académie des Sciences in 1701. The death of his wife plunged him into deepest sorrow, and the loss of his foreign pupils through the War of the Spanish Succession, reduced him to poverty. He died in Paris on April 3, 1717.
Ozanam was honoured more abroad than at home. He was devout, charitable, courageous, and of simple faith. As a young man he had overcome a passion for gambling. He was wont to say that it was for the doctors of the Sorbonne to dispute, for the pope to decide, and for a mathematician to go to heaven in a perpendicular line.