He was the son of John Ernuszt, a converted Jew, who started his career as a custom's duty collector during the reign of Matthias Corvinus, King of Hungary.

After the united armies of Corvinus's supporters were defeated in the battle of Bonefield, he swore fealty to Vladislaus II Jagiellon.

[5] Ernuszt was famed for his erudition among the Renaissance humanist scholars who visited Hungary in the late 15th century.

[8] The Székesfehérvár Chapter obstructed Ernuszt's canonical visitations to its estates in the Bishopric of Pécs and forbade the local priests from attending the episcopal synods.

[9] The chapter emphasized that its estates were exempt from the jurisdiction of all bishops in Hungary, but Ernuszt persuaded the Holy See to strengthen his authority over the parishes in question in 1478.

[13] Ernuszt seized Pécsvárad Abbey, which had been held by the absent Cardinal Ascanio Sforza,[14] but soon hurried to Buda to attend the Diet which assembled in late May to elect Matthias's successor.

[10][17] To prevent the coronation of Vladislaus, he and Lawrence Újlaki left Buda taking the Holy Crown of Hungary and the royal treasury with them.

[18][19] However, Vladislaus's supporters, Stephen Báthory and Paul Kinizsi, assembled their troops and defeated the united armies of Ernuszt and his allies at Gyönk on 4 July.

[20] The new king granted him John Corvinus's two former estates, Futak and Cserög (now Futog and Čerević in Serbia).

[23] Ernuszt entered into negotiations with Reinprecht von Reichenburg, the commanders of Maximilian's army in Hungary, but refrained from providing military assistance to him against Vladislaus' troops.

[23] Instead, he stayed at Pécs and Đurđevac and came to an agreement with Ladislaus Egervári, Ban of Croatia, over the mutual defense of their estates.

[26] The Thurzós and the banker Jakob Fugger established a joint venture, named Ungarischer Handel ("Hungarian Trade"), to exploit the mines.

[27] According to Antonio Bonfini, Ernuszt persuaded the king to launch a campaign against Lawrence Újlaki who had captured Futak and Cserög.

[21] Ernuszt remained Ban of Croatia, Dalmatia and Slavonia until 1498 and continued to preserve his seat at the Royal Council.

[9] Ernuszt was strangled in the summer of 1505[14] by his three retainers (including Albert Cupi, Dean of Baranya) who wanted to seize his wealth.

[31] The accounts contain a detailed record of the one-florin tax assessed in Hungary proper, Transylvania and Slavonia in 1494 and 1495 which was to be paid by each peasant household.