Van Mierop was a son of the Treasurer General of Holland, Vincent Cornelisz and Maria Ruysch.

From 1 June 1547, he was also a councilor in the Privy Council, an advisory body to the ruler at his appointment; this was Emperor Charles V. In 1556, he donated one of the stained glass windows in the Grote or Sint-Janskerk in Gouda, an image of Jesus preaching at the Jordan.

In 1557, Van Mierop provided an interest-free loan of 500 Carolus guilders to the Brothers of the Common Life of the Hieronymushuis on the Kromme Nieuwe Gracht.

A gallery was built from his house to the brothers' church and their 'librije,' where the cathedral provost had a prayer room for the rest of his life.

In 1562, he bought the knightly town of Huis te Vliet in Lopik.