From June 1933 to October 1934 he was the assistant medical director at Virchow Hospital in Berlin.
In 1935, he completed training as an expert for "race hygiene" at the Kaiser Wilhelm Institute for Anthropology, Human Genetics and Eugenics.
After this, he became the adjutant of the ministerial director Arthur GĂĽtt at the Reich Ministry of the Interior.
He was also the chief of staff at the SS Office for Population Politics and Genetic Health Care, which in 1937 became the SS Main Race and Settlement Office.
Poppendick was departmental head and staff leader of the Genealogical Office.
At the beginning of World War II, he was drafted as an adjutant to a medical department of the army and took part in the attack on Belgium, France and the Netherlands.
In November 1941, Poppendick was accepted into the Waffen-SS.
In 1943, Ernst-Robert Grawitz of the Reich Physician SS appointed him to lead his personal staff.
Poppendick joined the NSDAP in 1932 (party member No.
998607) and the SS (No.
36345).
He reached the rank of OberfĂĽhrer in the SS.
Poppendick was implicated in a series of medical experiments done on concentration camp prisoners, including the medical experiments done in RavensbrĂĽck.
At the American Military Tribunal No.
I on 20 August 1947 he was acquitted from being criminally implicated in medical experiments, but was sentenced to 10 years imprisonment for membership in a criminal organization, the SS.
He was released on 31 January 1951.
Later on, Poppendick managed to get his medical services paid by insurance, in Oldenburg.