He then worked in the Ministry of Foreign Affairs for 12 years, from 1941 to 1945 as head of the political-legal department and in 1945–48 as director.
[1] In June 1941, during the Occupation of Denmark, Hvass was tasked with assisting Minister of Foreign Affairs Erik Scavenius and director Nils Svenningsen in the negotiations with the Germans.
After 29 August 1943, he was involved in the work with trying to assist deported Danes in the prisons and concentration camps.
He played a central role in the establishment of the organisations that transported Danish, Norwegian and other prisoners to Denmark and Sweden in the spring of 1945.
His wife owned Hagestedgaard at Holbæk from 1953,[2] In 1972, he was appointed to honorary president of the International Institute of Administrative Sciences.