Stephen was the third son of King Béla the Blind and his wife, Helena of Rascia, born about 1133.
The earliest recorded event of Stephen's life occurred during the reign of his oldest brother, Géza II, who succeeded their father on 13 February 1141.
King Géza "granted ducal revenues to his brothers", Ladislaus and Stephen, according to the Illuminated Chronicle.
While the chronicle does not specify the date of this event, historian Bálint Hóman wrote that it happened in 1146.
 However, scholars Ferenc Makk and Gyula Kristó claim it was later, in about 1152, at the same time Géza II officially appointed his son, Stephen, as his heir.

According to the contemporaneous Rahewin, Stephen was "accused before the king of aspiring to royal power", along with Stephen's friends, and especially their uncle, Beloš.
In fear of being seized and executed by his brother, Stephen sought refuge in the Holy Roman Empire in summer 1157.

[Emperor Frederick I] held a diet at Regensburg, with a great attendance of princes, on the octave of Epiphany.
Among the many present there were ambassadors of [King Géza II of Hungary].
For his brother, [Stephen] by name, had by certain men been accused before the king of aspiring to royal power.
In this he was thought to have been instigated by Duke [Beloš], an uncle of them both, a very shrewd and scheming man, who seemed to be feeding the pride of a young man already accustomed to too much honor.
But the king, suspicious of the great attention paid to his brother, and fearing worse things from him than was needful, now openly accused not the man himself so much as his friends and those of his household, and turned all that they said or did against him.
After many accusations had been aired and many persons induced to bear false witness, the king was said to be planning to have his brother killed.
The latter, having learned that the Roman empire is an asylum for the whole world, escaped by fleeing to the emperor and tearfully bewailed his fate and his brother's bitter cruelty toward him.

— The Deeds of Frederick Barbarossa
Stephen was the third son of King Béla the Blind and his wife, Helena of Rascia, born about 1133. The earliest recorded event of Stephen's life occurred during the reign of his oldest brother, Géza II, who succeeded their father on 13 February 1141. King Géza "granted ducal revenues to his brothers", Ladislaus and Stephen, according to the Illuminated Chronicle. While the chronicle does not specify the date of this event, historian Bálint Hóman wrote that it happened in 1146.  However, scholars Ferenc Makk and Gyula Kristó claim it was later, in about 1152, at the same time Géza II officially appointed his son, Stephen, as his heir.
According to the contemporaneous Rahewin, Stephen was "accused before the king of aspiring to royal power", along with Stephen's friends, and especially their uncle, Beloš. In fear of being seized and executed by his brother, Stephen sought refuge in the Holy Roman Empire in summer 1157.
[Emperor Frederick I] held a diet at Regensburg, with a great attendance of princes, on the octave of Epiphany. Among the many present there were ambassadors of [King Géza II of Hungary]. For his brother, [Stephen] by name, had by certain men been accused before the king of aspiring to royal power. In this he was thought to have been instigated by Duke [Beloš], an uncle of them both, a very shrewd and scheming man, who seemed to be feeding the pride of a young man already accustomed to too much honor. But the king, suspicious of the great attention paid to his brother, and fearing worse things from him than was needful, now openly accused not the man himself so much as his friends and those of his household, and turned all that they said or did against him. After many accusations had been aired and many persons induced to bear false witness, the king was said to be planning to have his brother killed. The latter, having learned that the Roman empire is an asylum for the whole world, escaped by fleeing to the emperor and tearfully bewailed his fate and his brother's bitter cruelty toward him.
— The Deeds of Frederick Barbarossa
Stephen IV of Hungary