He was born in 1317,[1] as the second son of Thomas Szécsényi, Voivode of Transylvania and his first wife, an unidentified daughter of landowner Paul Visontai.

[1] As a younger son of his family, Szécsényi entered ecclesiastical career, which rapidly progressed due to his father's influence, who also became a relative to the Angevin dynasty after his second marriage to Anne, Duchess of Auschwitz.

[3] Szécsényi was elected Bishop of Vác on 11 October 1341, replacing Dominican friar Rudolph, who died in office.

For instance, he unlawfully occupied the half of ecclesiastical estates in the eastern side of the Eger valley, for which the chapter protested against him on 3 March 1365.

In 1367, Szécsényi handed over the Makovica Castle (today Zborov in Slovakia) to baron Peter Cudar for 200 gold ducats per year.

In December 1371, Szécsényi held a three-day synod in his diocese, dedicated to its patron saint John the Apostle.