Her family realized that her beauty was a great asset and raised enough money to send her to court with an unspoken yet precise aim of replenishing the family coffers from the royal bed. Marie arrived to the court of Louis XIV in 1678 and became the maid of honor to the Duchess of Orléans. Louis XIV was then torn in between the affections of Marquise de Montespan and Madame de Maintenon. Infatuated by the beauty of the young girl, the King suddenly abandoned both women. Now the stand-off between Athénaïs and La Maintenon was suddenly eclipsed by a new passion which appeared to threaten them equally. Despite her physical charm, Marie Angélique was, in the court parlance, "as stupid as a basket," This declaration made Montespan and Maintenon certain that Louis XIV would return to either one of them. Arrangements were quickly made, and, a few weeks after the presentation of the young girl to court, the king made her his new favourite royal mistress and presented entertainments in her honour.
Louis showed his great affection for Marie by wearing ribbons often matched to hers. This flattery spoiled her, and she began to consider herself as the Queen. She flaunted herself before Queen Marie Thérèse, and put Athénaïs de Montespan to shame with her behavior. The king gave her one hundred thousand crowns a month, twice as gifts, but he could not exhaust her extravagance, her coach was being driven by eight horses, it seemed to "eat her reign at a time." Louis XIV suddenly felt young again. He wore diamonds, ribbons and feathers. Every day they went out to a new party, ballets, and comedies—never had luxury been pushed so far.
Soon it appeared she was pregnant, causing the wrath of Madame de Montespan, who did not think the king was so enamoured of his young conquest. She thought their affair was a passing fancy, easily controlled and easily disposed of. She then said to Marquise de Maintenon, "the king has three pillars: my name, this girl and your heart."
Marie-Angélique created the famous fashion of Fontanges: during a hunt in the forest of Fontainebleau, her hair clung to a branch and she appeared before the king with her hair loosely tied in a ribbon, tumbling in curls to her shoulders. The king found this "rustic" style delightful. The next day, all the courtiers adopted this hairstyle, except the Marquise de Montespan, who thought her hairstyle was in "bad taste". The bitterness between Athénaïs and Marie went as far as Athénaïs releasing her two tame bears which she kept in a little menagerie Louis had given her in the grounds of the palace, and "accidentally," the two bears went to destroy Marie's apartment in Versailles. This event made both women comical at court.
In December 1679, Marie gave birth prematurely to a stillborn boy. She was then said to have been "wounded in the service." The king bestowed on her the title Duchess of Fontanges and a pension of 80,000 livres, however, in 1680, Louis began to tire of her. Still sick (suffering from serious blood loss) since the birth, she retired to the Abbey of Chelles, and did not appear at court again.