Marie de Gournay met Montaigne in Paris in 1588, when she was 23 and Montaigne 55 years old. He later visited her at her residence in the Château de Gournay. The first literary reference to Marie as Montaigne's "fille d'alliance" is in the Essays (chap. XVII, II). After her mother's death in 1591, Marie moved to Paris, leaving the family home to her brother Charles, who was forced to sell it in 1608. Montaigne died the following year, and his widow, Françoise de Montaigne, provided de Gournay with a copy of the Essays and charged her with its publication. Marie de Gournay did so, publishing the first posthumus edition of the Essays with a long preface praising Montaigne's ideas. Her translation of the Essays, is remarkable for fidelity in translating Latin sentences and Montaigne's highly specific references to classical and sometimes obscure texts.

In Paris, Marie de Gournay met Henri Louis Haber de Montmort and the scholar Justus Lipsius presented her to Europe as a woman of letters. De Gournay found herself protectors by writing for Queen Margo, Henry IV of France, Marie de Médicis, Louis XIII, the marquise de Guercheville, the ministers Villeroy and Jeannin, and Richelieu. She thus obtained the privilege of being able to publish her own work Richelieu and was awarded her a modest royal stipend. As a woman, Marie de Gournay was often subject to both personal attacks and unfounded criticism of her work. She never married and supported herself through her inheritance and work.

As a Catholic, she was hostile to the Protestant movement but remained close to libertines such as Théophile de Viau, Gabriel Naudé and François La Mothe Le Vayer, to whom she would leave her library, which she herself had received from Montaigne (who in turn had inherited it from La Boétie). In 1610 she engaged in the debate on the assassination of Henry IV, strongly defending the Jesuits.

Marie de Gournay was self-taught in Latin and Greek. She translated works by Sallust, Ovid, Virgil, and Tacitus. She wrote verses about her cat, Léonore (also the name of Montaigne's daughter) and Joan of Arc, adapted Ronsard, wrote on the instruction of princes, and criticized the Précieuses. She died on 13 July 1645, aged 79 and is buried at the Saint-Eustache Church in Paris.