Ozanam was the leading historical and literary critic in the neo-Catholic movement in France during the first half of the 19th century. He was more learned, more sincere, and more logical than Chateaubriand; and less of a political partisan and less of a literary sentimentalist than Montalembert. In contemporary movements, he was an earnest and conscientious advocate of Catholic democracy and of the view that the Church should adapt itself to the changed political conditions consequent to the French Revolution.

In his writings he dwelt upon important contributions of historical Christianity, and maintained especially that, in continuing the work of the Caesars, the Catholic Church had been the most potent factor in civilizing the invading barbarians and in organizing the life of the Middle Ages. He confessed that his object was to prove the contrary thesis to Edward Gibbon, and, although any historian who begins with the desire to prove a thesis is quite sure to go more or less wrong, Ozanam no doubt administered a healthful antidote to the prevalent notion, particularly amongst English-speaking peoples, that the Catholic Church had done far more to enslave than to elevate the human mind. His knowledge of medieval literature and his appreciative sympathy with medieval life admirably qualified him for his work, and his scholarly attainments are still highly esteemed.

His works were published in eleven volumes (Paris, 1862–1865). Volumes X and XI were dedicated to a selection of his letters. Ainslie Coates (London, 1886) translated into English volume X, freely available to download in this link: