The daughter of two musicians for the deposed King of Poland Stanislas Leszcynski whose court at Lunéville became famous as a cultural centre, Justine Duronceray was educated in dance, music and literature, and performed under the stage name Mlle Chantilly in 1744 at the Saint-Laurent Fair, Paris dancing the role of Laurence in Les Fêtes Publiques. In 1745 she married the theatre director Charles-Simon Favart who between 1746 and 1748 set up a company at the Theatre de la Monnaie de Bruxelles where she became a success dancing in works created by her husband.

On their return to Paris in 1749 she abandoned dancing in favour of acting at the Comedie Italienne, but was confined in a convent in 1750 after becoming the mistress of Maurice, Comte de Saxe, a Marshal of France and her husband’s patron. She returned to the stage after the death of the Marshal and became a great favourite at the Comedie Italienne where she was an advocate of realistic stage costume. Her life was fictionalised in Offenbach’s 1878 comic opera Madame Favart.