Stephen was the youngest of five sons born to Charles I of Hungary and his third wife, Elizabeth of Poland.
Of the five, Louis, Andrew and Stephen survived infancy.
Stephen was born on "the feast of St Stephen" (that is on 20 August) in 1332, according to the Illuminated Chronicle.
He was named for the first king of Hungary, Stephen, who had been canonized in 1083.
He was baptized by Archbishop Csanád Telegdi.
A priest of Bohemian origin, Ladislaus, was one of his tutors.

Stephen was first mentioned in a royal charter of his father on 12 May 1339.
In the document, he was styled as Duke of Slavonia, but he did not assume direct government of the province: the bans (or governors) continued to govern Slavonia on the king's behalf.
In July, Stephen's maternal uncle, Casimir III of Poland, named Stephen's mother and father or one of their sons as his heir if he died without a legitimate heir.
Decades later, the Polish historian, Jan of Czarnków, claimed that Charles had decided to secure a throne for each of his sons and wanted to make Stephen his heir in Hungary.
Next year, a Venetian envoy recorded that Charles was planning to visit Dalmatia along with his wife and "their younger son" who must have been Stephen.

Charles I died on 16 July 1342.
During the first years of the reign of his brother, Louis, Stephen was only sporadically mentioned in official documents.
At Stephen's request, the judge royal, Paul Nagymartoni, deferred a hearing in 1343 and exempted a nobleman of paying a fine in 1344.
Stephen was regularly mentioned in his brother's charters of grant from May 1345, evidencing that he had become a member of the royal council.

Stephen's brother, Andrew, who had married Joanna I of Naples, was murdered on 18 September 1345.
Louis I of Hungary accused Joanna of staging the plot against Andrew.
Louis entered into correspondence with Pope Clement VI, demanding her punishment.
From early 1346, Louis also urged the pope to grant the Kingdom of Naples to him or to Stephen.
The pope styled Stephen as duke or duke of Transylvania in his letters addressed to Louis, but the Hungarian documents consequently referred to him as the "duke of all Slavonia" in 1345 and 1346.
Louis conquered significant territories during his first campaign in southern Italy in 1347 and 1348, but after he returned to Hungary, Joanna and her second husband, Louis of Taranto, expelled Louis' troops from most fortresses.
Stephen was the youngest of five sons born to Charles I of Hungary and his third wife, Elizabeth of Poland. Of the five, Louis, Andrew and Stephen survived infancy. Stephen was born on "the feast of St Stephen" (that is on 20 August) in 1332, according to the Illuminated Chronicle. He was named for the first king of Hungary, Stephen, who had been canonized in 1083. He was baptized by Archbishop Csanád Telegdi. A priest of Bohemian origin, Ladislaus, was one of his tutors.
Stephen was first mentioned in a royal charter of his father on 12 May 1339. In the document, he was styled as Duke of Slavonia, but he did not assume direct government of the province: the bans (or governors) continued to govern Slavonia on the king's behalf. In July, Stephen's maternal uncle, Casimir III of Poland, named Stephen's mother and father or one of their sons as his heir if he died without a legitimate heir. Decades later, the Polish historian, Jan of Czarnków, claimed that Charles had decided to secure a throne for each of his sons and wanted to make Stephen his heir in Hungary. Next year, a Venetian envoy recorded that Charles was planning to visit Dalmatia along with his wife and "their younger son" who must have been Stephen.
Charles I died on 16 July 1342. During the first years of the reign of his brother, Louis, Stephen was only sporadically mentioned in official documents. At Stephen's request, the judge royal, Paul Nagymartoni, deferred a hearing in 1343 and exempted a nobleman of paying a fine in 1344. Stephen was regularly mentioned in his brother's charters of grant from May 1345, evidencing that he had become a member of the royal council.
Stephen's brother, Andrew, who had married Joanna I of Naples, was murdered on 18 September 1345. Louis I of Hungary accused Joanna of staging the plot against Andrew. Louis entered into correspondence with Pope Clement VI, demanding her punishment. From early 1346, Louis also urged the pope to grant the Kingdom of Naples to him or to Stephen. The pope styled Stephen as duke or duke of Transylvania in his letters addressed to Louis, but the Hungarian documents consequently referred to him as the "duke of all Slavonia" in 1345 and 1346. Louis conquered significant territories during his first campaign in southern Italy in 1347 and 1348, but after he returned to Hungary, Joanna and her second husband, Louis of Taranto, expelled Louis' troops from most fortresses.
Stephen of Anjou