Louis the Great died on 10 September 1382. Cardinal Demetrius, Archbishop of Esztergom, crowned Mary “king” with the Holy Crown of Hungary in Székesfehérvár on 17 September, a day after her father’s burial. Mary’s title and her rapid coronation in the absence of her fiancé, Sigismund, show that her mother and her mother’s supporters wanted to emphasize Mary’s role as monarch and to postpone or even hinder Sigismund’s coronation. The queen mother, Elizabeth, assumed regency and most of Louis’s barons preserved their offices.
All royal charters issued during the first six months of Mary’s reign emphasized that she had lawfully inherited her father’s crown. However, most Hungarian noblemen were strongly opposed to the very idea of a female monarch. They regarded Charles III of Naples as Louis the Great’s legitimate heir because Charles was the last male offspring of the Capetian House of Anjou.
To strengthen Mary’s position, the queen mother wanted her to marry Louis, the younger brother of Charles VI of France and their engagement was announced in May 1385.
Charles III of Naples landed in Dalmatia in September 1385. Sigismund of Luxembourg invaded Upper Hungary (now Slovakia), forcing the queen mother to give Mary in marriage to him in October. However, they could not prevent Charles from entering Buda. After Mary renounced the throne, Charles was crowned king on 31 December 1385, but he was murdered at the instigation of Mary’s mother in February 1386. Mary was restored, but the murdered king’s supporters captured her and her mother on 25 July. Queen Elizabeth was murdered in January 1387, but Mary was released on 4 June 1387. Mary officially remained the co-ruler with Sigismund, who had meanwhile been crowned king, but her influence on the government was minimal.
Mary was pregnant when she decided to venture out alone on a hunt in a Buda forest on 17 May 1395. Her horse tripped, threw her and landed on top of her. The trauma induced labor and she gave birth prematurely to a son. The queen succumbed to the fatal injuries; being far from any kind of assistance, her son died as well. She was buried in the cathedral of Várad (now Oradea in Romania).
According to the 1383 agreement between their mother and the Polish lords, Jadwiga was her childless sister’s heir in Hungary. Vlad I of Wallachia, a Hungarian vassal, issued an act of submission on 28 May, acknowledging Jadwiga and her husband as Mary’s legitimate successors. The widowed king’s close supporter, Stibor of Stiboricz, expelled Vlad from Wallachia. Władysław-Jogaila gathered his troops on the Polish-Hungarian border, but the invasion of Hungary was stopped. On 8 September, the most influential Hungarian lords declared that they would not support any change in government while Sigismund was far from Hungary fighting against the Ottoman Turks. Before the end of the year, peace negotiations between the representatives of Hungary and Poland ended with an agreement. Jadwiga adopted the title “heir to Hungary”, but she and her husband took no further action against Sigismund.