Thomas was born in Forst (Lausitz), Brandenburg. The factory owner's son and later general joined Infantry Regiment 63 as an ensign and a career soldier in 1908. From 1928, he dealt with armament questions at the Army Weapons Office in the Reich Defence Ministry in Berlin. Thomas continued to work as the Chief of Staff for the Army Weapons Office in the Reich Defence Ministry from 1928-1938, where he intensively studied the dynamic of national economics and war preparations, pushing forward the idea of a "defense economy" - that is, the marshaling of Germany's resources for the purpose of war under a central planning commission. Despite his misgivings with National Socialism following the dismissal of Colonel General Baron Werner von Fritsch on trumped up allegations of homosexuality, Thomas remained an important member of the German General Staff. Nevertheless, it was upon von Fritsch's removal in 1938 that Thomas experienced his first major inner conflict with National Socialism. It is speculated that he stayed aboard from here forward to foment plans for a coup. In 1939, he became head of the Defence Economy and Armament Office in the "Oberkommando der Wehrmacht" (OKW). He was a member of the board of Kontinentale Öl AG (an oil company whose purpose was to exploit petroleum resources in occupied countries) as well as "Reichswerke Hermann Göring", a major iron and steel company.