In 1940, as a sign of protest against the Nazi occupation of Luxembourg he closed his legal firm, and became a manual labourer in Karelshaff near Colmar-Berg.
As a member of the Resistance, he was imprisoned in October 1943 in the Grund, and was later interned in Hinzert concentration camp for 18 months.
After escaping in March 1945, he hid until the end of the war.