Petro (or Petru) was born into the Movilă family, the Movilești, which had been granted noble status in the Polish-Lithuanian Commonwealth in 1593. His father Simion and his uncle Ieremia had been variously Princes (or "Hospodars") of Wallachia and Moldavia.
After his family's Moldovan fortunes fell, Petro took refuge in the Ruthenian Voivodeship of Poland. He received a typical education for an aristocrat of his time, learning Latin, Greek, Polish, Church Slavonic, and Ruthenian. He was equally comfortable writing in Ruthenian, Slavonic, and Polish, and could produce on demand the allusions to classical Roman writers and to Greek and Roman mythology that were demanded by the florid prose style of his day.
As a member of the nobility, he brought a "legitimacy" (at least in the eyes of his fellow aristocrats) to the position of Metropolitan of Kyiv.