[8] He was the youngest son of a Croatian lesser nobleman, Grgur Utješenović, and Anna Martinuzzi, who was descended from a Venetian patrician family.

[20] The Diet of Hungary elected the wealthy Count John Zápolya—the son of Martinuzzi's patroness, Hedwig—king in November, but the most powerful barons ignored this decision and proclaimed Ferdinand of Habsburg the lawful monarch in December.

[21] A civil war broke out and a supporter of Ferdinand, Gáspár Serédy, pillaged the Sajólád Monastery shortly before Martinuzzi returned to Hungary.

[24] He acted as John's personal envoy and visited Hungary three times to convince the expelled king's supporters—including Stephen Báthory of Somlyó, Jakab Tornallyai and Pál Ártándy—to remain loyal to him.

[28] Gritti's other henchman, János Dóczy, murdered the popular bishop of Várad (now Oradea in Romania), Imre Czibak, in August 1534.

[32] Tamás Nádasdy deserted John Zápolya for Ferdinand of Habsburg after Martinuzzi deprived him of the administration of the salt mines in Máramaros County in 1534.

[34] In this year, Ferdinand's emissary, Johann von Wese, noted that the "White Monk" (Martinuzzi) had taken full control of the negotiations.

[35] Martinuzzi wanted to reach an agreement, but he could also prove himself determined to refute any compromise in order to strengthen John's position during the negotiations, especially after a new war broke out between Ferdinand's brother, Emperor Charles V, and King Francis I of France.

[37] Martinuzzi hinted that he was willing to support Ferdinand and proudly claimed that he was the only politician to be able to mediate between the "Ottomans, Serbians, Moldavians, Wallachians and Hungarians", according to Wese's notes.

[37] The secret Treaty of Várad acknowledged the provisional division of Hungary between János and Ferdinand, but it also prescribed that the kingdom was to be reunited as soon as one of the two kings died.

[38] Martinuzzi started emphasizing that the treaty could be regarded valid only after the Diet enacted it and prevented the most powerful barons from confirming it.

[32] The two voivodes (or royal governors) of Transylvania, Imre Balassa and István Majláth, concluded a secret agreement with the leading Transylvanian lords in December 1539.

[44] The delegates accused Martinuzzi of tyranny, stating that his officials had levied arbitrary taxes and unlawfully forced the Transylvanian noblemen to contribute to the erection and maintenance of royal fortresses.

[45] He stood by his treasurer, emphasizing that Martinuzzi had levied taxes to secure the paying of the annual tribute to the Ottoman Empire.

[40] Franjo Frankopan, Péter Perényi, Ferenc Bebek, István Ráskay and Martinuzzi's other personal enemies informed Charles V that they were willing to support Ferdinand I to reunite Hungary if the emperor promised to provide military assistance to his brother against the Ottomans.

[51] After Martinuzzi garrisoned his own retainers in Buda Castle, gossips about his attempts to seize full control of the government were spreading in the queen's court.

[51] The sultan's envoy, Çavuş Sinan, tried to persuade the delegates of the Three Nations to acknowledge Mailáth as the voivode of Transylvania at Berethalom (now Biertan in Romania) in September.

[55] Ferdinand's envoys, Elek Thurzó and Ferenc Révay, came to Buda in October, but the queen did not abandon John Sigismund's claim to Hungary.

[56] Ferdinand's envoy, Niklas zu Salm, offered the region of Pressburg and Nagyszombat (now Bratislava and Trnava in Slovakia) to John Sigismund in return for Buda, but Martinuzzi refused.

Martinuzzi frustrated attempts by dowager queen Isabella Jagiellon to promote Ferdinand; the latter, contending that John II's election had violated the treaty, invaded Hungary, and an Austrian army reached the walls of Buda in 1541.

This led to the 29 December 1541 Treaty of Gyalu, in which Ferdinand received western Hungary; the Eastern Hungarian Kingdom (an independent principality under Ottoman suzerainty) was reverted to John Sigismund.

The regent imprisoned the queen in Gyulafehérvár (now Alba Iulia), drove the hospodars out of Transylvania, and defeated the Turks at Déva (now Deva).

This agreement was confirmed by the diet of Kolozsvár (now Cluj-Napoca) in August 1551; Martinuzzi remained governor of Transylvania, and was ordained Archbishop of Esztergom.

Although Hungary was again reunited, Ferdinand's inability to defend it against the Ottomans forced Martinuzzi to resume the payment of tribute to the sultan in December 1551.

When the Ottomans seized Csanád (now Cenad) in 1551, Martinuzzi and imperial generals Giambattista Castaldo and Sforza-Pallavicini joined forces against a common foe.