Léopold Blondiau is one of the founders and the first president of the "Cercle des Anciens de l'Ecole Moyenne A" (1907). Being active in the industrial sector and a veteran, he became municipal councilor for the liberal party in Etterbeek (Brussels) in 1927 and, later, responsible for public education for the same commune after the second World War. He was also vice-president of the Red Cross, vice-president of the "Comité d'Entr'aide" and board member of the "Foyer Etterbeekois".

Léopold Blondiau was a fervent advocate of public schools and he will follow all the hstory of "his" school, the "Athénée Robert Catteau". He can still be found as honorary vice-president of the "Amis et Anciens de l'Athénée Robert Catteau" in 1980, date of his death.