He became the leading theologian of the Reformed Protestant movement of the Palatinate, serving both at the University of Heidelberg and the College of Wisdom (Collegium Sapientiae).

At age fifteen he enrolled at the University of Wittenberg, boarding for the next seven years with Philipp Melanchthon, the erudite successor of Martin Luther.

He was a lifelong protégé of the prominent imperial physician Johannes Crato von Krafftheim, who likewise hailed from Wrocław.

The Wrocław opponents' vitriolic reaction succeeded in driving him out of the city to Zurich, where he became friends with Zwingli's successor Heinrich Bullinger and the Italian Reformer Pietro Martire Vermigli.

[4] Ursinus's collected catechical lectures (Het Schatboeck der verclaringhen over de Catechismus) was one of the most prominent theological handbooks among seventeenth century Reformed Christians and was especially popular in the Netherlands.