The enthusiasm shown by the Count de Maistre for the Roman Catholic Church awakened a deep interest in Madame Swetchine. This interest was greatly enhanced by the admirable examples of piety and charity set before her in the lives of several of the French exiles in St. Petersburg, with whom she had contracted friendships. Especially was she impressed and attracted by the amiable virtues of the Princess de Tarente, the devout elevation of her character, and the triumphant sanctity of her death. Madame Swetchine at length resolved to make a deliberate examination of the claims of the Roman Church, and to come to a settled conclusion. Providing herself with an appropriate library, acompanied only by her adopted daughter Nadine, in the summer of 1815, she withdrew to a lonely and picturesque estate, situated on the borders of the Gulf of Finland. Here, through the days and nights of six months, she plunged into the most laborious researches, historical and argumentative. The result was, that she became convinced of the apostolic authority of the Roman primacy, and avowed herself a Catholic. Soon after this conversion, the Jesuits were ordered to leave Russia. Indignant at an order which she regarded as unjust, she openly identified herself with the cause of these proscribed missionaries. The machinations of the political enemies of General Swetchine had made his situation disagreeable to him; and, when he saw those enemies gaining credit, his pride took offence, and he determined to leave the country. Madame Swetchine's passion for travel and observation combined with her new religious faith to make this removal less unwelcome than it would otherwise have been.
The close of the year 1816 found her established in Paris, where, with the exceptions of a year in Russia, and a couple of years in Italy, she was to reside until her death. The Bourbon nobility, now recalled to France, and reinstated in power, repaid the generous kindness she had shown them in St. Petersburg, by giving her a hearty welcome, and lavishing attentions and affection on her. Her deep interest in charitable institutions soon brought her into intimate and most cordial relations with De Gerando. Baron Humboldt and the Count Pozzo di Borgo, among the earliest to become her friends, were assiduous visitors at her house; and, in the salon of the brilliant Duchess de Duras, where she was quickly appreciated and made to feel at home, she became acquainted with the most interesting and commanding minds of France at that time, such as Chateaubriand, Remusat, Cuvier, Montmorency, Villemain, Barante. These persons have all testified, in turn, to the great impression her character made on them.