In Vietnam, he worked to improve relations between the United States and South Vietnamese Prime Minister Ngo Dinh Diem.

[citation needed] Reinhardt began his professional career serving on the United States and Mexico International Boundary Commission.

[22] In October 1941, as Moscow came under threat from the German army as a result of Operation Barbarossa, Reinhardt remained in the city under Llewellyn Thompson (the then Second Secretary at the U.S. Embassy to the Soviet Union),[23] while Ambassador Laurence A. Steinhardt and other diplomatic personnel and news correspondents were evacuated to Kuibyshev.

When on 19 November 1951, the NATO Defense College opened its doors to Course 1 in Paris, Reinhardt was the only civilian senior instructor assigned to the course.

[28] During the spring of 1953 President Eisenhower asked Reinhardt to participate as a Russian expert as part of a top-secret program, named Project Solarium, examining the advantages and disadvantages of a series of military and political strategies seeking to "roll back" existing areas of Soviet influence and restore the prestige of the west.

[34] Following his departure from the State Department, Reinhardt accepted a position with the Stanford Research Institute to run its office in Zurich, Switzerland.

[37] On September 10, 1949, Reinhardt married Lillian Larke "Solie" Tootle of Bethany, West Virginia at a ceremony in Weston, Connecticut.

[40] They had four children: George Frederick ("Fred"), Anna Aurelia ("Aura"), Charles Henry ("Harry"), and Catherine Jane ("Cathy").

[35][45] He was buried at the Protestant Cemetery in Rome (Il Cimitero Acattolico di Roma), for which he had served as administrator from 1961 until 1968, by virtue of his post as U.S.