After Sigismund Vasa was elected king in 1587, Báthory convinced his cousin's advisors to send reinforcements to Poland to fight against Maximilian of Habsburg, who also claimed the throne.

[3] Isabella and John Sigismund ruled the eastern territories of the medieval Kingdom of Hungary as vassals of the Ottoman Sultan Suleiman the Magnificent.

[4] The date of Andrew's birth is uncertain, because his actual age was kept secret in the early 1580s to promote his career in the Roman Catholic Church.

[3] Andrew and his youngest brother, Balthasar, and their sisters, Anne and Catherine, lived for years at their stepfather's estate, Érmihályfalva (now Valea lui Mihai in Romania).

[6] Both his mother and her second husband were Lutherans, but Andrew remained Roman Catholic, like his father and uncles, Christopher and Stephen Báthory.

[14] Giovanni Andrea Caligari, the papal nuncio (or ambassador) in the Polish–Lithuanian Commonwealth, urged the king to persuade Andrew to start a church career.

[23] He visited Charles Borromeo, archbishop of Milan, who was a highly respected prelate and regarded as a living saint for his piety in his diocese.

[24] A Protestant retainer of Andrew, Ferenc Forgách, converted to Catholicism in the Basilica della Santa Casa in Loreto on 21 November.

[36] Samuel Zborowski's brothers (he had been executed on Stephen Báthory's orders), wanted to capture and murder Andrew, but their plan failed because of a flood.

[42] Andrew, his brother Balthasar, and their cousin Sigismund Báthory, prince of Transylvania, were among the sixteen candidates to the throne of Poland and Lithuania.

[43] Before long, Bartosz Paprocki published a pamphlet against "the kings from Hungary", accusing Stephen Báthory of suppressing the Polish nobles.

[55] Andrew went to Transylvania and sent letters to Rome to achieve a reconciliation, emphasizing that the Jesuits' aggressive proselytizing policy had contributed to their unpopularity in the predominantly Protestant principality.

[59] The new papal nuncio, Annibale di Capua (who was their supporter) convinced the king to nominate Jerzy Radziwiłł to the see after Myszkowski died on 5 April 1591.

[65] In August 1591, Maximilian of Habsburg, who still claimed Poland and Lithuania, sent his envoy to Andrew seeking Transylvanian support against Sigismund III.

[66] Andrew emphasized that being under Ottoman suzerainty, Transylvania could not openly support Maximilian, but he also promised that Sigismund Báthory would not prevent the mustering of Transylvanian soldiers to fight in Poland.

[66] In the same month, Sigismund Báthory's plan to enable the Jesuits to return to Transylvania gave rise to a serious family conflict, because both Andrew and Balthasar refused to support the prince at the Diet.

[69][70] The Holy See also tried to reach a compromise on the Kraków bishopric, but Jan Zamoyski, who was in conflict with the king, persuaded Andrew to give up his claim in favor of Radziwiłł.

[75] The prince was ready to join the alliance, but Andrew and Balthasar emphasized that Transylvania could not secede from the Ottoman Empire without the participation of Poland in the coalition.

[76] Most of Sigismund's advisors supported their proposal, but his confessor, the Jesuit Alfonso Carillo, convinced him to continue the negotiations with the Holy Roman Emperor, Rudolph II.

[78] Sigismund Báthory's maternal uncle, Stephen Bocskai, and other commanders of the Transylvanian army, persuaded the prince to get rid of those who did not support the Holy League.

[85] At the pope's request, Sigismund Báthory allowed Andrew's mother and Stephen's wife, along with their children, to move to Poland.

[87] Andrew exchanged letters with Aaron the Tyrant, Voivode of Moldavia, who had been captured by Sigismund Báthory because of his attempts to make peace with Poland and the Ottoman Empire.

[89] Sigismund III of Poland summoned Andrew and Stephen before the Senate, but Pope Clement VIII intervened on the brothers' behalf.

[90] After the Ottomans defeated the armies of the Holy League in a series of battles in 1596, Transylvanian noblemen sent letters to Andrew, offering him the principality.

[91][92] After realizing that neither the pope nor the Polish king would support him against Sigismund Báthory, Andrew declared that he was ready to make peace with him.

[102][103] However, as Alfonso Carillo noted, the most influential noblemen remained opposed to Andrew, even if they did not dare to raise an objection openly.

[102] Instead of them, Andrew had to choose his officials from among the Roman Catholic lords: he made István Bodoni ispán (or head) of Kolozs County and Gáspár Sibrik the commander of the cavalry.

[104] For instance, Gáspár Kornis remained a member of the royal council, although he had played a preeminent role in the execution of Andrew's brother in 1594.

[105] Andrew also started negotiations with the Ottoman Empire, demanding the confirmation of his hereditary rule and his suzerainty over Wallachia, and refusing the payment of the tribute for six years.

[106] After the marriage of Sigismund Báthory and Maria Christierna of Habsburg (who was a cousin of Rudolph II) was declared invalid in August, Andrew proposed himself to her.