His permanent honorary title of "magister" demonstrates his university degree (possibly he studied in Sorbonne or other Paris-type cathedral schools, gaining rhetorical and legal erudition).

[2] In contemporary records, he is first referred to as a cleric by Pope Innocent IV on 20 February 1245, when he authorized papal legate Giacomo da Pecorara to permit Sixtus' consecration and to grant him the right of possession of church benefices despite his "lack of origin".

[6] Besides his duty to proclaim the Scripture readings used in the Liturgy of the Word, Sixtus was responsible for management of the cathedral school of Esztergom and teaching the clerics and the poor scholars, in accordance with Canon 18 of the Third Council of the Lateran (1179).

On 15 July 1264, Pope Urban IV ordered Vincent, Bishop of Nyitra (or Nitra) to provide a dignity and benefice for Sixtus either in Zagreb or other cathedrals, or perhaps in a church of the Archdiocese of Esztergom, because he "wants to leave" his position of archdeacon in Komárom (probably due to its extensive administrative obligations).

At first, he was sent to Italy in 1258 to represent King Béla's interests at the Roman Curia, as some of his policies gave rise to many conflicts between the Hungarian royal court and the Holy See after the Mongol invasion.

[13] Sixtus sold some part of his inherited land in Hetény to his relative and neighbour Mikó Szécs, in order to finance his diplomatic mission to Rome.

At the same time, the king was angered by the fact too that Pope Urban allowed his opponent Cardinal Báncsa to be free to distribute Timothy's benefices in Hungary among his relatives.

For his loyal service, Sixtus was granted royal land donations from his monarch and spouse Queen Maria Laskarina in Hetény and Radvány (present-day Radvaň nad Dunajom, Slovakia) after returning home, when the civil war broke out.

[17] In 1270, Sixtus was among the members of the Hungarian delegation presumably led by magister Ákos sent to Naples which escorted the then twelve-year-old princess Mary to marry Charles the Lame.

[5] For Charles of Anjou, Hungary was an important ally, when he forged alliances in the Balkan Peninsula to counteract the surrounding great powers, the Byzantine Empire and the Republic of Venice.