Stibor descended from a Polish noble family of the Clan of Ostoja whose possessions were located around Bydgoszcz in Greater Poland; his father was Mościc, Voivode of Gniewkowo.

Following the king's death (10 September 1382), the Dowager Queen Elisabeth, who governed the two kingdoms in the name of his daughters, made Stibor the governor of Kuyavia and Łęczyca in Poland in 1383.

A few years later he expanded his small empire with castles and properties in Dioś, Szomolya, Szent Vid, Suran, Maniga, Baganya, Zuk, Kreesztes, Rarkov, Bary, Koszonic, Rakovitz, Tatkolch, Ratkolch, Ilkaman, and Dévény in Nyitra and Presburg counties.

But Stibor and the Clan, returned with their army to, together with Nicholas II Garai, renounce the possession of most of castles and finally, the members of the Royal Council set the King free on 29 October 1401.

Shortly afterward, Stibor led the negotiations with the Teutonic Knights who bought the Neumark (in the Margraviate of Brandenburg) from Sigismund on 25 July 1402.

[3] Again, in 1403, there was uprising against Sigismund led by Archbishop John Kanizsai of Esztergom that offered the Hungarian crown to King Ladislaus of Naples.

Shortly afterwards, the King appointed Stibor to the head of Nyitra county and entrusted him to govern the possessions of the Archdiocese of Esztergom and the Diocese of Eger (1405).

As Sigismund wished to sell Neumark (Brandenburg) in order to reinforce the economy, Stibor set up a plan to make the Teutonic Knights to pay a much higher price than expected, keeping in mind that they would not then be able to finance a bigger army against Poland.

A problem for the Teutonic Knights arose when they were notified that Stibor was to be in charge of selling Neumark to Poland for a much smaller amount of money.

But it would be surely to be understood to put pressure on the Teutonic Knights to buy the property since they could not afford to be surrounded by Polish forces from the west.

A loss such as that would be remarkably high keeping in mind that Stibor owned almost half of present-day western Slovakia at the time of negotiations.

It is significant that all those penalties that had been paid to the Polish Crown as compensation for losses in the Grunwald war, ended in Hungary and the treasury of King Sigismund on the basis of diplomatic work by Stibor of Stiboricz and Zawisza Czarny.

Secret meetings and agreements between Hungary and Poland and so between the Sigismund and Jogaila, using their most trusted couriers, question wherever there was ever any serious dispute between both ruling Kings.

[10] In the end, it was the Clan of Ostoja that was the leading force in breaking down the Teutonic side, they did it not only by using the fine art of the sword but also with outstanding diplomatic skills.

This reinforced Sigismund's finances and made it more difficult for the Teutonic Knights to hire mercenaries to fight on their side against the Poles-Lithuanians in Grunwald-Tannenberg.

Because of the diplomatic work of Stibor of Stiboricz, Sigismund abandoned hostile actions against Poland and turned to support the wealthy and mighty Teutonic Knights by signing never executed agreements in to order to gain financial benefit to protect his own Empire for the Ottoman threat.

At the end of 1411, Stibor, his brothers and other members of the Clan of Ostoja were in charge of leading troops to fight against the Republic of Venetia in Friuli.

In 1412, Stibor was meeting with Zawisza Czarny (The Black Knight) in his Castle of Lubló (today Stará Ľubovňa), preparing the negotiation between Sigismund and Polish King Vladislav Jogaila, which ended with the Treaty of Lubowla.

Stibor of Stiboricz's two brothers, Andrew and Nicholas, and their sons, also held high offices, land and castles in the northern region of the Kingdom of Hungary, as well as lesser holdings in Poland.