Daughter of the unwealthy tax-collector Louis de Robertier Denis Lalive de Bellegarde and his wife Marie Dickx Josèphe Prouveur, Sophie married Claude Constant César, Comte d' Houdetot, an army brigadier, at the
Saint-Roch church in
Paris on 28 February 1748. She was presented at court, an honor reserved for ladies of a certain nobility and social distinction. She mingled in literary circles in Paris, aided by her cousin and sister-in-law,
Louise d'Épinay, who was in a relationship with
Frédéric Melchior, baron de Grimm, editor of the handwritten literary journal in which
Diderot circulated much of his work. Mme d'Épinay often helped with editorial work and was part of the coterie around Diderot, Grimm and the
Baron d'Holbach. The Comtesse d'Houdetot gave birth to three children, one of whom, César Louis Marie François Ange d'Houdetot, became an army brigadier like his father and was governor of
Martinique during the
French Revolution. Her acquaintances praised Sophie d'Houdetot for her generosity and intelligence rather than for her beauty. A friend in later years,
Claire Élisabeth de Rémusat, said of her: "One can hardly go further than Madame d'Houdetot, I would say not so much in kindness as in benevolence." The Baron de Frénilly, who knew her in the 1790s, described her as "the good, amiable, and eternally young Vicomtesse d'Houdetot ... a laugher at etiquette, cheerful, vivacious, witty, prolific in ingenious thoughts and happy phrases" despite "an ignoble ugliness, a raucous voice, and a treacherous eye which was always looking sideways when it seemed to be looking you in the face."
Jean-Jacques Rousseau gave this description of her in his
Confessions: == Relationship with Rousseau ==