The idea of a female monarch remained unpopular among the Hungarian noblemen, the majority of whom regarded Mary's distant cousin, Charles III of Naples, as the lawful heir.

To strengthen Mary's position, the queen mother wanted her to marry Louis, the younger brother of Charles VI of France.

Sigismund of Luxembourg invaded Upper Hungary (now Slovakia), forcing the queen mother to give 14-year-old Mary in marriage to him in October.

[3][4] Since Louis had fathered no sons, the expectation that he would bequeath Hungary, Poland, and his claims to the Kingdom of Naples and Provence to his daughters made them desirable spouses for members of the European royal families.

[7] The leading Hungarian and Polish lords confirmed Louis's promise of Mary's and Sigismund's marriage on 14 April 1375.

[11] Louis summoned the Polish prelates and lords to Kassa (now Košice in Slovakia) in September 1379, persuading them to acknowledge Mary's right to succeed him in Poland.

[5][12] The contemporaneous Jan of Czarnków, who was biased against Louis, recorded that the Poles yielded to the monarch's demand only after he had prevented them from leaving the town by shutting its gates.

[15] According to the historian Oscar Halecki, Louis wished to divide his kingdoms between his two surviving daughters, [16] but Pál Engel and Claude Michaud write that the ailing king wanted to bequeath both Hungary and Poland on Mary and Sigismund.

[19] Most of Louis's barons preserved their offices; the queen mother only dismissed the master of the cupbearers, George Czudar, and his brother Peter, voivode of Ruthenia.

[28] On the latter occasion, in response to Queen Elizabeth's demand, the noblemen also promised that they would not pay homage to anyone else than either Mary or Jadwiga.

[29] Bodzanta, Archbishop of Gniezno, the Nałęcz family, and their allies in Greater Poland favoured a native prince, Siemowit IV of Masovia.

[28] To avoid a civil war,[19] Queen Elizabeth sent envoys to the Polish noblemen's next assembly which met in Sieradz in late February 1383.

[30] Her envoys absolved the Poles from their 1382 oath of loyalty to Mary on 28 March, announcing that the queen mother would send her younger daughter, Jadwiga, to Poland.

[26] The royal army marched to Croatia and laid siege to Vrana, forcing John of Palisna to flee to Bosnia.

[26] The negotiations of Mary's marriage in France caused a new rift within the Hungarian nobility, because the Lackfis, Nicholas Zámbó and Nicholas Szécsi and other high officers, who had been appointed during Louis the Great's reign, continued to support Mary's fiancé, Sigismund, in accordance with Louis the Great's will.

[41] Louis I of Anjou died on 10 September 1384, enabling his rival, Charles III of Naples, to stabilize his rule in Southern Italy during the next months.

[42][38] The consolidation of Charles III's position in Naples also contributed to the formation of a party of noblemen who supported his claim to Hungary.

[38][43] John Horvat, Ban of Macsó (now Mačva in Serbia), and his brother, Paul, Bishop of Zagreb, were the leading figures of their movement.

[49] She also sent letters to Zagreb and other places in the kingdom, forbidding the local inhabitants to support Lackfi, Nicholas Szécsi, Bishop Paul Horvat and their relatives.

[49] John and Paul Horvat and their allies formally offered the crown to Charles III of Naples and invited him to Hungary in August.

[51] Sigismund stormed into Upper Hungary, accompanied by his cousins, Jobst and Prokop of Moravia, and occupied Pozsony County.

[54] Mary and her mother received him ceremoniously before he reached Buda, and he entered the capital in the two queens' company in early December 1385.

[18] According to the contemporaneous Lorenzo de Monacis, Mary and her mother, who attended Charles's coronation, visited Louis the Great's tomb during the ceremony where they burst into tears because of their ill fate.

[59][60][61] They persuaded Blaise Forgách, the master of the cupbearers, to join them, promising him the domain of Gimes (now Jelenec in Slovakia) if he murdered the king.

[67] Queen Elizabeth, who according to the 15th-century historian Johannes de Thurocz was "driven by folly", decided to visit the southern counties of the kingdom that were controlled by supporters of Ladislaus of Naples.

[70] Elizabeth took all the blame for the rebellion and begged the attackers to spare her daughter's life, according to Johannes de Thurocz's account.

[73] One of his supporters, Ivan of Krk, laid siege to Novigrad Castle with the assistance of a Venetian fleet, which was under the command of Giovanni Barbarigo.

[77] Nevertheless, according to Johannes de Thurocz, Mary persuaded her husband to dismember John Horvat who was captured in July 1394 although Sigismund would have been willing to spare his life.