He belonged to a family of Angoumois, which could trace its descent back to the 13th century; charters carry the history of the house two centuries further. For some generations before the historian the family had been distinguished, both in the army and in the field of science. Montalembert's father, Marc René, had fought under Condé, and subsequently served in the English army; he married Elise Rosee Forbes, and his eldest son, Charles, was born in London. At the Restoration of 1814 Marc René returned to France, was raised to the peerage in 1810, and became ambassador to Sweden (where Charles completed his education) in 1826. He died in 1831, a year after the overthrow of the monarchy.
Charles de Montalembert was under twenty-five and therefore too young to take his seat as a peer, but he retained other rights. Combined with his literary and intellectual activity, this made him a person of some importance. He was a Liberal, in the English sense, and disagreed with the new regime on only the religious question; he would have approved of the policy of the golden mean represented by Louis Philippe. He wished to see the Church free from state control and attacked the monopoly of public instruction by which the monarchy fortified its position. This latter scheme first brought Montalembert into notice as he was formally charged with unlicensed teaching. He claimed the right of trial by his peers, and made a notable defence with a deliberate intention of protest (1832).
On the other hand, he thought that the Church should not obstinately oppose new ideas. He had eagerly entered into the plans of his friends, Lamennais and Lacordaire, and collaborated with them in the newspaper, L'Avenir. The Ultramontane party was roused by their boldness, and Montalembert and his two friends then left for Rome. This pilgrimage proved useless to mitigate the measures which the Roman curia took against L'Avenir. Its doctrines were condemned in two encyclicals (Mirari vos, 1832, and Singulari vobis, 1834), and Montalembert submitted. He clung to his early Liberalism, and in 1848 saw the end of a government towards which he had always been hostile. He had a seat in the Chamber of Deputies till 1857, but was then obliged to retire into private life. He was still recognized as a formidable opponent of the empire. Meanwhile his Liberal ideas had made him some irreconcilable enemies among the Ultramontanes. Louis Veuillot, in his paper, L'Unitiers, opposed him. Montalembert answered by reviving a review which had for some time ceased publication, the Correspondent (1855), in which he set himself to fight both against the fanatical party of Pope Pius IX and the Syllabus, and the more or less free-thinking Liberals of the Revue des deux mondes.
He took great interest in the débuts of the Liberal empire, whilst trying to parry the blow which the Ultramontanes were preparing to deal to Liberal ideas by proclaiming in the Vatican council the dogma of papal infallibility. But once again he would not allow himself to be seduced from obedience to the pope; he now severed his connection with Pere Hyacinthe Loison as he had with Lamennais, and made the submission expected of him to the council. It was his last fall. Broken down by the trial of these continued fights against people of his own religion, he died prematurely.
In addition to being an eloquent orator, Montalembert wrote a style at once picturesque, fiery and polished. He was an ardent student of the Middle Ages, but his medieval enthusiasm was strongly tinctured with religious sentiments. His first historical work, La Vie de Ste Elisabeth de Hongrie (1836), is not so much a history as a religious manifesto, which did much to restore the position of hagiography. It met with great success; but Montalembert was not elected a member of the Académie française till later, after the fall of the July monarchy (January 9, 1851).
From this time he gave much of his attention to a great work on monastacism in the West. He was at first attracted by the figure of St Bernard, and devoted one volume to him; this was, however, afterwards withdrawn on the advice of his friend Dupanloup, and the whole edition was destroyed. He then enlarged his original plan and published the first volumes of his Moines d'occident (1860), an eloquent work which was received with much admiration in those circles where language was more appreciated than learning. The work, which was unfinished at the time of the author's death, was completed later from some long fragments found among his papers (vols. vi. and vii., 1877).
Montalembert married Mlle de Merode, daughter of Félix de Mérode. His daughter married the vicomte de Meaux, a Roman Catholic statesman and distinguished writer.