The kinship originated from the gens (clan) Becsegergely, thus his distant relatives were the Bethlen and Apafi families, future royal houses of the Principality of Transylvania.

It is possible that his father died in that year, becoming Anthony and his brother John Somkeréki as joint heads of the household in Somkerék (today Șintereag, Romania).

[5] Erdélyi was made castellan of Knin Fortress by 1401 (when his lord Garai held the dignity of Ban of Croatia and his father-in-law John Antimus functioned as vice-ban).

[11] In that capacity, he successfully defended the castle against Hrvoje Vukčić Hrvatinić, the partisan of claimant Ladislaus of Naples, who besieged Knin in that year.

[5] For his courageous engagement in Knin, while Sigismund was imprisoned, Erdélyi was granted the villages of Harina, Bilak (Herina and Domnești in Romania, respectively) and the uninhabited Nécs in July 1402.

Erdélyi stayed in Bohemia until the next year, when Sigismund had to abadon his claim temporarily due to Ladislaus of Naples' invasion to Southern Hungary.

[13] Returning Hungary, Erdélyi was donated the confiscated lands, fields, meadows and mill of the disloyal John Kolman for his Bohemian military service in May 1403.

He received huge land donations in June 1405: Gernyeszeg, Sáromberke, Sárpatak, Unoka and Körtekapu (today Gornești, Dumbrăvioara, Șapartoc, Onuca and Poarta, respectively) became properties of the Erdélyi family.

[13] As a member of the escort of Nicholas Garai, Erdélyi traveled to Germany and was present at the coronation of Sigismund as King of the Romans took place in Aachen on 8 November 1414.

Traveling further to Italy, Erdélyi also took part in the initial phase of the Council of Constance at the turn of 1414 and 1415, and acted as majordomo of Garai's court.

[13] For his loyal service, he was granted the privilege of building a castle in one of his estates by Sigismund at the national diet of Tétény (today Budafok-Tétény) in August 1410.

[19] A month later, Antipope John XXIII permitted Anthony Erdélyi and his wife, Clara to receive full forgiveness from all confessors on the territory of the Diocese of Transylvania.

For instance, Szécsényi intended to build a mill at river Mureș (Maros), whose operation threatened Erdélyi's neighboring lands, Gernyeszeg and Sáromberke with flooding.

Erdélyi, as a lesser nobleman, was much richer than most of his neighbors because of his influential relationships, thus he was able to lend large sums for pledged landholdings, further increasing his family's estates and wealth.