 After World War II, Grewe taught at the University of Göttingen from 1945 to 1947 and then in Freiburg im Breisgau from 1947.In 1943 Grewe married Marianne Partsch.Wilhelm Grewe served under Konrad Adenauer in the post-war years, from 1951 to 1955, heading the delegation negotiating the end of Allied occupation of West Germany, which led to the signing of the Convention on Relations between the Three Powers and the Federal Republic () in 1954.