Art historian and conservation scholar. Marijnissen was born in Ghent but at an early age lost the sight in his right eye from a serious ulcer. Despite this, Marijnissen studied art history and in 1948 wrote a dissertation on the Patronage of Philip II under Paul Coremans. However the technical aspects of art, rather than archival research, caught his attention. Cormans teaching led Marijnissen to join the initiative to restore L'Agneau Mystique (The Lamb of God) and issue a publication on it.
He was appointed to the Institut Royal du Patrimoine Artistique (IRPA, Royal Institute for Cultural Heritage), Brussels, as Assistant Director, overseeing the Conservation Department under his mentor, Coremans. Unfortunately relations between the two men became strained when the actual duties for Marijnissen's position and their friendship ultimately ceased. After Coremans death in 1965, Marijnissen defended his dissertation the following year. He published his a revised version of his dissertation, Dégradation, conservation, restauration de l'œuvre d'art, (Degradation, Conservation and Restoration of Works of Art) in 1967.
Marijnissen employed a connoisseurship method in his work. He devoted much of this scholarly energies to determining fakes. His scholarly opinions could be at odds with the mainstream; he chose not to take sides in the debate of when Brueghel's Fall of Icarus was painted in the artist's career, a view which John White. chided as a moment when "warning bells should really ring."
- White, John. Pieter Bruegel and the Fall of the Art Historian 56th Charlton Lecture, University of Newcastle upon Tyne, 1980;
- "Mélanges en l’honneur de Roger Marijnissen: Portrait de Maître" CeROArt June, 2015, https://journals.openedition.org/ceroart/4801