During World War II Schiltz was a member of the Nationaal-Socialistische Jeugd Vlaanderen (National Socialist Youth Flanders).
He studied law, economic science and Thomistic philosophy at KU Leuven, where he became a member of the Katholiek Vlaams Hoogstudentenverbond (Catholic Flemish Students Union).
He participated in drawing up the 1977 Egmont pact, which was seen as treason by more hard line advocates from the Flemish Movement.
In that year, he resumed practising law, first with Ernst & Young and Peeters Advocaten, later he founded Laurius-Schiltz-Verschoeven ADVC.
Willem-Frederik Schiltz, his son by his second marriage, is an Open Flemish Liberals and Democrats politician who has served as a Belgian Senator and as a member of the Flemish Parliament (a language/community based parliament that emerged from the state reforms the senior Schiltz helped introduce).