At the age of 15 Marie-Jeanne moved to Paris, where, using the name Jeanne Rançon, she worked first as an assistant to a young hairdresser named Lametz (with whom she had a brief relationship which may have produced a daughter), then as a companion to a lonely aristocrat, Madame de la Garde, and later as a milliner's assistant in a shop named 'A La Toilette' owned by a certain Monsieur Labille, where she became a very good friend of his daughter, the future famed painter Adélaïde Labille-Guiard. As reflected in art from the time, Jeanne was a remarkably attractive blonde woman. Her beauty came to the attention of Jean du Barry, a high-class pimp/procurer and owner of a casino, in 1763. He made her his mistress and helped establish her career as a courtesan in the highest circles of Parisian society, enabling her to take several wealthy men as her benefactors.
She first became a courtesan known as Mademoiselle Lange, immediately becoming a sensation in Paris, building up a large aristocratic clientele. The dashing Maréchal de Richelieu became one of her recurring customers. Jean du Barry, however, saw her as a means of influence with Louis XV, who became aware of her in 1768 while she was on an errand at Versailles which involved the Duc de Choiseul, who found her rather ordinary, in contrast to what most other men thought of her. In any case, Marie-Jeanne could not qualify as an official royal mistress unless she had a title; this was solved by her marriage to Du Barry's brother, Comte Guillaume du Barry, in 1769. She was presented to the King's family and the court on April 2, 1769, wearing a queenly and bedazzling silvery white gown brochaded with gold, huge paniers at the sides, which had been ordered especially by Richelieu himself. Jeanne was now attended by her personal Indian page Zamor, given to her by Louis XV, and wore extravagant gowns of great proportions both in size and cost. With diamonds covering her delicate neck and ears, she was now the dauphin's maîtresse déclarée. Due to her new role in Court, she made both friends and enemies, Her most bitter rival was the Comtesse Béatrix de Grammont, Choiseul's sister, who tried her best to acquire the late Madame Pompadour's place in the King's bed.
While Jeanne was part of the faction that brought down Duc de Choiseul, Minister of Foreign Affairs, she was unlike her late predecessor Madame de Pompadour in that she had little political influence upon the king, but rather preferred to pass her time having new gowns made and ordering jewelry of every shape, size and colour.
While Jeanne was known for her good nature and support of artists, she grew increasingly unpopular because of the King's financial extravagance towards her. Her relationship with Marie Antoinette, the Dauphine of France, was contentious. The Dauphine supported Choiseul as the proponent of the alliance with Austria and also defied court protocol by refusing to speak to Madame Du Barry, due not only to her disapproval of the latter's background, but also after hearing of du Barry's amused reaction to a story told by Cardinal de Rohan, in which Marie-Antoinette's mother, Maria Theresa, was slandered. What was to many an amusing incident had now become a phenomenon at Versailles, where courtiers anxiously waited to see if the new Dauphine would speak with du Barry when they found themselves under the same roof. She was once humiliated, according to one account, when Madame Adelaide quickly intervened to silence Marie Antoinette as the latter opened her mouth to speak to du Barry. The King's mistress was outraged, heading back in fury to complain to Louis XV. Eventually, during a ball on New Year's Day 1772, Marie Antoinette spoke to the Favorite, saying, "There are a lot of people at Versailles today," but she made it clear to Mercy the very next instant that she would say nothing else to Madame du Barry.
At the king's request before his death in May 1774, du Barry was banished from the court and sent to the convent of Pont-au-Dames, as her continued presence at Versailles would have prevented the king from receiving absolution. Two years later she moved to the Château de Louveciennes, where she continued her career as a courtesan, having liaisons with both Henry Seymour and Louis Hercule Timolon de Cossé, Duke of Brissac.
In 1792 du Barry made several trips to London on the pretext of recovering stolen jewelry, with the aid of her now-grown page, Zamor, who disliked his mistress for her airy attitude. In addition, she was suspected of financially assisting emigrés from the French Revolution. The following year, she was arrested by the Revolutionary Tribunal of Paris on charges of treason. While in prison, her cell-mate was fellow courtesan Grace Elliott. After a trial, du Barry was executed by guillotine on the Place de la Concorde on December 8, 1793. She had tried to save herself by revealing the hiding places of the gems she had hidden around her property.
On the way to the guillotine she continually collapsed in the tumbrel and cried "You are going to hurt me! Why?!" She became quite hysterical during her execution: "She screamed, she begged mercy of the horrible crowd that stood around the scaffold, she aroused them to such a point that the executioner grew anxious and hastened to complete his task." Her last words to the executioner: "Encore un moment, monsieur le bourreau, un petit moment," ("One moment more, executioner, one little moment") were her most famous. Her remains were briefly placed in the Chapelle Expiatoire in Paris but were later moved to an unknown location.
The jewels she had smuggled out of France to England were sold by auction at Christie's in 1795 for the not inconsequential sum of £8,791 4s 9d. However, since she was dead and had no known heirs, the proceeds went to the Tribunal in Paris.
The necklace involving Jeanne de la Motte-Valois, which was the same one that the dauphine Marie Antoinette was innocently accused of bribing Rohan to purchase for her, was originally destined for Madame du Barry by Louis XV, who died before the purchase could take place, leaving the jewellers Bohmer and Bassenge desperate for a buyer of the overly-expensive trinket. On this subject, see also Affair of the Diamond Necklace.