Little is known about the earliest youth of Peter Parler. His father, Heinrich Parler the Elder, was a stonemason at Cologne Cathedral. Around 1333, when Peter was born, Heinrich was invited by the free imperial city of Schwäbisch Gmünd to take over construction of a large new parish church, Holy Cross Minster. Peter was already working alongside his father on the church when the cornerstone of the choir was laid in 1351. This is presumably also where his apprenticeship was completed. The division of the choir by a continuous balustrade demonstrates what would become his trademark style. The arched section at the southern portal of the church can also be attributed to Peter. The designs developed by the father and son team at Holy Cross were unique and mark an important milestone in late Gothic architecture and sculpture.

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Peter then set off on the so-called "Wandering Years" (German: Wanderjahre), the Medieval German tradition of working as a travelling craftsman after completing apprenticeship. On these visits he learned the most important concepts of Gothic construction techniques in Central Europe. He visited Cologne, perhaps Paris, and certainly spent time in Strasbourg – precise knowledge of Strasbourg Cathedral can be seen in his subsequent buildings. While working in Cologne he met Druda (Gertrud), daughter of the resident architect Bartholomäus von Hamm. They eventually married and had four children: three sons, of which two went on to become known master builders in their own right, and a daughter.

While undocumented, some scholars believe Parler traveled to England during this period, while others find the possibility unlikely. The idea arises because certain detailed and concealed technical devices appear in his later work which could have only been obtained through first-hand experience and not from any architectural drawings. What is definitely known is that masons at Strasbourg implemented specific craft methods from western England in the late 1200s, which points to knowledge of English Gothic architectural methods in the Rhineland. Since Peter Parler spent time working at Strasbourg, it is much more likely his knowledge of these methods came from there. In particular, the vaults he later designed at St. Vitus Cathedral were most probably modeled after the St. Catherine Chapel of Strasbourg Cathedral.