	Kőszegi was unanimously elected Bishop of Győr by the local cathedral chapter between May and October 1308, following the death of his predecessor Theodore Tengerdi. Despite the opinion of some scholars, his election took place without any direct pressure from the Kőszegis. Contemporaries, including papal legate, Gentile Portino da Montefiore did not question the legitimacy of his election in the upcoming years, albeit it could be a sign of political flexibility. Kőszegi spent the following months in the escort of the papal legate, who arrived to Buda by 2 November 1308. Kőszegi attended the Diet on 27 November 1308, when Charles was unanimously proclaimed king. He also participated in the second coronation of Charles on 15 June 1309, also representing his family. His papal nomination promoted only after the treaty between Charles I of Hungary and Henry Kőszegi on 4 June 1309 (Ivan Kőszegi died by then), when members of the family, including Bishop Nicholas, took an oath of allegiance to the king. One of Henry's conditions for the king's acceptance was the retention of bishopric of Győr for the family through his natural nephew, Nicholas. Thereafter, Pope Clement V confirmed his election on 28 July 1310, describing Kőszegi as "solutus" and "soluta", i.e. natural son of free and unmarried men, a 28-year-old clergyman. The pope also determined his "servitium commune" in 800 golden florins. Sometimes between March and July 1311, Kőszegi was consecrated as bishop by Thomas, Archbishop of Esztergom.