His inclination, however, was to writing novels, and the success of his romance L'Ariane in 1632 led to his formal admission to a circle of writers that met at the house of Valentin Conrart.
His success led to official preferment, and he was made conseiller du roi, contrôleur-général de l'extraordinaire des guerres, and secretary-general of the fleet of the Levant.
His long epic Clovis (1657) is noteworthy because Desmarets rejected the traditional pagan background, and maintained that Christian imagery should supplant it.
In his later years Desmarets devoted himself chiefly to producing a number of religious poems, of which the best known is perhaps his verse translation of the Office de la Vierge (1645).
He was an outspoken opponent of the Jansenists, against whom he wrote a Réponse à l'insolente apologie de Port-Royal (1666).