De Wasseige served in the 10th Notre Dame de Fontgalland scout unit during World War II. He was a volunteer for the entire war and celebrated the Liberation of Belgium in 1944. He earned a degree in economics from the Catholic University of Leuven in 1951 and subsequently worked at a Hainaut-Sambre steel plant from 1958 to 1975. He then became a business delegate for the and was also a member of the "Esprit" group, where several political analysts of different views met in Wallonia and Brussels, such as .