 An early member of the Rexist movement, Matthys took over the editorship of the party newspaper, "Le Pays Réel", in 1936 and in May 1941 was promoted to director of propaganda.He became official leader of Rex that same July after Léon Degrelle left to serve in the Waffen SS.He was nominated for the position as he was a weak character who posed no real threat to Degrelle's position as leader.