He was born into a family of presumed Italian origin, which possessed lands and villages in the Banate of Severin, the southeastern part of the Kingdom of Hungary.

Ladislaus' cousins, Thomas, Paul and Nicholas played an active role in restoring and strengthening royal power against the oligarchs along the southern border of the kingdom.

It is plausible that he is identical with that Minorite friar, who was referred to as King Charles' royal chaplain and personal confessor by a document issued in the Kingdom of Naples on 7 January 1316.

Peter became the new Bishop of Bosnia,[7] while Jánki – as the candidate of the Hungarian monarch – was appointed his superior, the Archbishop of Kalocsa by Pope John XXII on 3 July 1317, after the annulment of the former election of Demetrius Vicsadoli.

[9] He was consecrated as bishop by Nicolò Albertini, the Cardinal-bishop of Ostia in the papal court on 15 August 1317 and was granted his pallium too by four additional cardinals.

Joining the royal army, he participated in the siege of Komárom (now Komárno in Slovakia); Charles' troops successfully captured the fort from the powerful oligarch Matthew Csák in November.

After Charles neglected to reclaim Church property that Matthew Csák had seized by force, the prelates of the realm – archbishops Thomas, Ladislaus Jánki and their eleven suffragans – summoned a national synod to Kalocsa and made an alliance in the spring of 1318 against all who would jeopardize their interests.

Upon their demand, Charles summoned a diet immediately to the field of Rákos in summer and commissioned his ispáns and castellans to recover Church property in their territory.

[15] According to historian Ildikó Tóth, the close cooperation between the prelates lasted until the death of Archbishop Thomas in early 1321; he was succeeded by the king's brother-in-law, Boleslaus.

Jánki was one of the four prelates, who excommunicated John, abbot of Pilis and monk Nicholas for their violent actions against the parsonage of Budakalász in September 1326.

Later, Jánki's successors considered it a disadvantageous contract and blamed the late archbishop that he had exchanged rich estates in Upper Hungary for humble uninhabited lands in the southern frontier; they have been trying to recover the lost goods for decades.

[4] As archbishop, Jánki owned the royal castles of Krassova and Érsomlyó (present-day Carașova in Romania and Vršac in Serbia, respectively) as "office fiefs" (or honors).

[2] A royal charter, dated to 6 October 1335, narrated that Charles had sent Jánki, to Clisura Dunării three times in 1334 and 1335 to make preparations for the movement of Bogdan.

In 1333, the monarch requested Pope John XXII to declare that the coronation ceremony must be performed by the archbishop of Esztergom, unless his possible illness or absence.