Delahaut went to the Academy for Fine Arts in Liège and was also a doctor in art history. He was the first geometric abstract artist in Belgium after 1945. During his whole career he defended his artistic principles by means of paintings and writings. In 1946 he became a member of the Jeune Peinture Belge where he was the only abstract painter. At the Salon des Réalités Nouvelles in Paris in 1947 he also stood up for abstraction. In 1952 he was a founding member of the group Art Abstrait. Afterwards he joined the groups Formes (1956) and Art Construit (1960).In 1954 he was a co-signer of the Manifeste du Spatialisme. His oeuvre developed itself according to a strictly distinctive serial logic in which pure forms dialogue in a game of contrasting coloured facets. He also experimented with spatial constructions.