Marnix Gijsen (20 October 1899 – 29 September 1984) was a Belgian writer. His real name was Joannes Alphonsius Albertus Goris; his pseudonym relates to Marnix van Sint Aldegonde and the surname of his mother (Gijsen).
Gijsen was born in 1899 in Antwerp, Belgium. In his youth he received a strict Roman Catholic education, at the Jesuit college of Saint Ignacio in Antwerp, but in 1917 he was punished heavily (consilium abeundi, E: 'advice to leave') for his militant Flemish activism during World War I. In 1925 he went to the Catholic University of Leuven, where he obtained a PhD in history and moral sciences with a dissertation on Études sur les colonies marchandes méridionales (portugaises, espagnoles, italiennes) à Anvers de 1488 à 1567. He went on to study at the University of Freiburg, Paris (Sorbonne) and London (London School of Economics).