Born to ethnic German parents in Torosovo (also called Hoffnungsfeld), near Odessa, in the Zebrikovo district of the Ukraine. It is probable, during his lifetime, he was the world's foremost scholar on the subject of Volga Germans.
In 1918, Leibbrandt studied theology in Germany; also taking classes in philology and history. In 1927, he was awarded a Ph.D. He traveled extensively through the Soviet Union in 1926, 1928, and 1929. During his visits, he was variously represented as a doctor of philosophy, a post-graduate student, a professor of history from Leipzig University, and an employee of the Institute for the Study of Germans Abroad (Deutsches Ausland Institute) in Stuttgart. The official purposes of his visits were the study of the history of the development of German colonies in the Black Sea coastal region and the gathering of historical information. As a result of his work, a book regarding emigrant movement of the Germans was published in Germany.
Leibbrandt had a talent for languages; which, coupled with a Rockefeller scholarship, enabled him to resume his studies in Paris and the United States from 1931 - 1933. While in the U.S. he kept contact with Volga Germans who had also emigrated to America.
Leibbrandt accepted a request from Alfred Rosenberg in 1933 to return to Germany, and joined the Nazi Party that year. He was then named director of the Eastern Division of the Foreign Policy Office of the NSDAP. He was also placed in charge of anti-Soviet and anti-Communist propaganda. When the Soviet Union was invaded in 1941, and the Ministry for the Eastern Occupied Territories was established, Dr. Leibbrandt was chosen by Rosenberg to direct the Political Department. Thus, Leibbrandt became the liaison for the Ukrainian, Caucasian, Russian, and other groups of emigres. Leibbrandt and Alfred Meyer attended the Wannsee Conference in 1942; representing the Ostministerium. In the summer of 1943, for unknown reasons, he ceased his duties in the Ministry and joined the Kriegsmarine (German Navy).
Leibbrandt was kept in Allied internment from 1945 - May 1949. He was formally charged with involvement in the murder of Jews, January 1950, by the Nuernberg Landgericht. The case against him was dismissed on August 10, 1950 and he was released from custody. In the post-war period, he returned to America and resumed his earlier studies on the subject of the Volga Germans; making expert contributions to the Association of Germans from Russia until his death in Bonn on June 16, 1982.