In January 1919, he returned to Mecklenburg and joined the Freikorps "von Brandis," seeing action in Upper Silesia and the Baltic states until his capture and imprisonment by the Red Army in Riga in July 1919.

In September 1925, he became a member of the National Socialist Working Association, a short-lived group of north and northwest German Gauleiter, organized and led by Gregor Strasser, which unsuccessfully sought to amend the Party program.

[4] He was elected to the Reichstag in September 1930 as a deputy for electoral constituency 35 (Mecklenburg) and served there until the fall of the Nazi regime.

After the Nazi seizure of power, he was named Reichskommissar for the Free States of both Mecklenburg-Schwerin and Mecklenburg-Strelitz on 24 March 1933.

He was subsequently elevated to the new post of Reichsstatthalter (Reich Governor) of Mecklenburg-Schwerin, Mecklenburg-Strelitz and the Free City of Lübeck on 26 May 1933.

From 1933 to 1934, Hildebrandt also served as the leader of the Nordische Gesellschaft (Nordic Society), which sought to strengthen German-Nordic cultural and political cooperation.

[7] In a letter to the chancellery, he expressed his concern about the lack of slave labourers, and said the problem could be avoided if "enough Russians are delivered later."

During a meeting with the Reich Defense Committee on 17 March 1942, Hildebrandt said "... for the Führer and for Adolf Hitler's cause, I pursue the law, even if it comes down to dead bodies."

[9] Between 1946 and 1948, Soviet military occupation authorities repeatedly demanded Hildebrandt's extradition over his involvement in the euthanasia murders in Sachsenberg.

[10] Nevertheless, in 1947, Hildebrandt and six others were found guilty of their involvement in the murders of several downed American airmen at the Dachau trials.

The other, Fritz Schröder, was sentenced to 20 years in prison due to his lesser involvement and the judges concluding that he was a reluctant participant.