Her mother was an lady-in-waiting in service to the queen from 1725, and her father reportedly "wasted his substance on actresses and the capacious requirements of Court life".

[1] In 1729, her mother died and Louise Julie replaced her as lady-in-waiting, Dame du Palais, to the queen and became first the mistress to the Marquis de Puysieux.

Louise Julie de Mailly was described as a thin beauty, with a perfect oval face and dark eyes with marked eyebrows, which gave her a “provocative and sensuous charm”.

[1] She knew how to adjust the fashion to suit her, designed her own “piquant and suggestive” negligees, and often wore her diamonds in her carefully dressed black hair – she was, however, not graceful but rather clumsy in her movements.

[1] As a person, she was described as good-tempered, witty and entertaining at social occasions, without being so at the expense of others, and as a loyal and devoted friend and a passionate and sincere lover, ready to sacrifice herself to make those she cared for happy.

[1] She completely lacked ambition and interest in politics, and genuinely “wanted nothing but the love of Louis XV, whom she adored with all the strength of her passionate nature”.

She nevertheless was regularly paid per sexual encounter with King according to the memoirs of the Marquise de Argenson[1] Louis XV reportedly appreciated her adoration and love for him and was satisfied with the fact that she was afraid of Cardinal Fleury, never trying to interfere in politics.

[1] There was speculation at court as to the mistress's identity: it was only known that she visited his private apartments at night, wearing a hood over her face in order not to be identified by anyone she met in the corridors on her way to and from his rooms.

To find out who she was, in the summer of 1738 Gabriel Bicheher stopped Mailly one night on her way to the king's bedroom and knocked her hood off, watched by two of the queen's ladies-in-waiting posted nearby.

After this she was given rooms next to the king's apartments and appeared as his hostess at his private parties at the Royal castles at Versailles, Choisy and La Muette.

[2] Louise Julie de Mailly was widely celebrated at court after she was introduced as the king's official mistress, but this put a great deal of strain their relationship.

Her new position exposed her to public criticism, and Louis XV reportedly felt humiliated when some regarded her as insufficiently beautiful for her role.

Louise Julie was devoted to her family and it was said of her that she was "a loving, sincere little creature with all the qualities of an easy dupe, and she was happy to Introduce her sisters at Court for the sole reason that it gave them pleasure".

The king and Louise Julie were both devastated by the death of Pauline-Félicité and shocked by the mutilation of her body; in her despair she was said to have performed a Catholic rite of penitence by washing the feet of the poor.

Marie Anne was described as "magnificently beautiful", dignified and graceful, with fair hair, "a complexion so white and pure that it glowed", large blue eyes and red lips with a "childlike smile"; she was also considered a charming wit who frequently used irony.

This she did most effectively; letters of a very passionate nature were exchanged; the lady dispatched those which she received to Richelieu, and in due course they were brought to the notice of Marie Anne de La Tournelle, who, furious at her young duke's deceitfulness, turned her attentions to the king and agreed to the suggestion of Richeliu and Soubise.

[1] Although the queen retracted her approval, Marie Anne was appointed to the position on 19 September,[2] and the next day, Cardinal Fleury refused Louise Julie's compensatory future post as dame d'atours of the dauphine.

She refused intercourse until he had proved his love by agreeing to provide her with the title of Duchess; a personal income to secure her future; a house "as sumptuous as Madame de Montespan’s had been", where she would be able to entertain the king in accordance with royal standards; an assurance than any children born of the union would be provided for and legitimized; to be properly courted before consent, and the dismissal of her sister, his official mistress, from court, and she herself officially acknowledged in her place.

[1] During his courting of Marie Anne, he reportedly treated Louise Julie more and more coldly, sitting in silence through their meals, taking to her only about his hopes to seduce her sister, causing her to cry.