He was part of the Jastrzebiec ancestral line of the szlachta (noble families) of Poland.

The first verified mention of Andrzej Jastrzębiec dates back to 1354, when he was listed among the parochs in Mazovia.

After a brief time spent as a missionary in the pagan Grand Duchy of Lithuania, he moved to the royal court of Hungary, where he became the confessor to Elizabeth of Poland, Queen of Hungary.

As an effect of his mission, on 31 July 1370 a new bishopric of Seret was created and the following year Andrzej became its first bishop.

In 1388, king Władysław II of Poland sent Andrzej with a mission to baptise Lithuania.