De Pomis was born in Lodi, Lombardy. He was apparently a pupil of the Venetian Jacopo Tintoretto. From 1588 to 1595, before coming to Graz, de Pomis served as the chamber painter to Ferdinand II, Archduke of Austria in the Tyrol (not to be confused with Ferdinand II, Holy Roman Emperor who was de Pomis's subsequent patron). On 25 October 1595 de Pomis married Judith Anna Dermoyen, the daughter of a Dutch court tapestry master. In that same year his son Johannes Baptist came into the world. He was followed by his sister Elisabeth in 1596. De Pomis and his wife had a total of 13 children; some of whom died at a young age. Both sons Johannes Baptist and Johann Nikolaus died in the Long Turkish War.