Musius is thought to have been born in Delft on 11 June 1500 (although the sources are not unanimous, some giving alternative dates or locations).

He studied theology at Leuven University, and travelled in Flanders and France, spending time in Ghent, Arras, Paris and Poitiers.

He then became rector of the Sint Agathaklooster in Delft, a post he held for 35 years, while writing Latin verse and corresponding with numerous scholars he had met on his travels.

On contravening a curfew for members of the Catholic clergy and religious orders, leaving the city to bring church treasures to safety, he was hunted down by the Lord of Lumey and transported to Leiden.

His sufferings were described in Richard Verstegan's Theatrum crudelitatum (Antwerp, 1587) and in book 10 of Petrus Opmeer's Historia martyrum Batavicorum (Cologne, 1625).