She was the daughter of the émigré Comte de Flavigny. In 1827 she married Col. Charles d'Agoult, 20 years her senior. She had early shown strength of will and enthusiasm for justice and freedom, and her marriage disappointed her. After meeting the composer Franz Liszt (Liszt, Franz), she decided in 1834 to run away with him. Their relationship, which produced several children, lasted until 1839 (they permanently separated in 1844).

Returning to Paris in 1839, Mme d'Agoult began her career as a writer and in 1846 published a largely autobiographical novel, Nélida. She was a close friend of the novelist George Sand (Sand, George), whose views on morals, politics, and society she shared and in whose house she had lived for a time with Liszt. She also became the leader of a salon where the ideas that culminated in the Revolution of 1848 were discussed by the outstanding writers, thinkers, and musicians of the day. Her own writings include Lettres républicaines (1848); Histoire de la révolution de 1848 (1850–53); a play, Jeanne d'Arc (1857); and a dialogue, Dante et Goethe (1866). Her Mes Souvenirs 1806–1833 (1877) was supplemented by Mémoires, 1833–1854, published posthumously in 1927; both are valuable for the light they throw on the social, literary, and musical circles of her time.