He issued a pamphlet in justification of the iconoclastic movement Beeldenstorm which devastated many churches in Flanders in 1566, and on the Duke of Alba's arrival next year had to flee the country.

After spending some time in Friesland and in the Electorate of the Palatinate he was in 1570 taken into the service of William, prince of Orange, and in 1572 was sent as his representative to the first meeting of the States-General assembled at Dordrecht.

He was sent as the representative of the insurgent provinces to Paris and London, where he attempted in vain to secure the effective assistance of Queen, Elizabeth I of England.

Attacked by the English and by his own countrymen for this act, he retired from public affairs and, save for a mission to Paris in 1590, lived henceforth in Leiden or on his estate in Zeeland, where he worked at a translation of the Bible.

His daughter Elizabeth married Sir Charles Morgan, a Welsh mercenary serving with the Dutch States Army who ended his career as Governor of Bergen op Zoom.

St. Aldegonde, or Marnix (by which name he is very commonly known), is celebrated for his share in the great development of Dutch literature which followed the classical period represented by such writers as the poet and historian Pieter Hooft.

His interest in cryptography possibly shows in the Wilhelmus, where the first letters of the couplets form the name Willem van Nassov, i.e. William 'the Silent' of Nassau, the Prince of Orange, but such acrostics - and far more intricate poetic devices - were a common feature of the Rederijker school in the Lowlands.