During the German invasion of Belgium, he looked after the casualties at the hospital of Antwerp before being evacuated, bringing along two large bags of books which he refused to leave behind.

It was not until 1943 that he produced his first photograph with a distinctive personal vision, "De Sade à Lénine", an image of a woman cutting a slice of bread, the loaf gripped tightly against her naked torso, the blade pointing at her left breast.

It was pure Surrealism, marked with the two themes that would characterize his photography: the everyday object stripped of its traditional function and the female body as an instrument of creation.

[6] Although Marien worked as an artist across many media, some of the most notable achievements throughout his career were as a chronicler of the Belgian Surrealists' activities and a publisher of their writings.

In 1954 he founded the magazine, Les Lèvres Nues,[3] and directed his review Le Ciel Bleu with Christian Dotremont and Paul Colinet.

He published the writings of such Belgian Surrealists as Paul Nougé, Louis Scutenaire and André Souris, as well as Magritte himself, in a series that eventually extended to hundreds of titles.

In 1979, Marien published L'Activité Surréaliste en Belgique, a chronological record of all the documents, manifestos, tracts and articles pertaining to the surrealist movement in Belgium that appeared between 1924 and 1950.

Presented as written by Magritte himself, it announced drastic discounts on the artist's major paintings and offered the chance to order them in different sizes.