Nadolny joined the German diplomatic service in 1902 and was deployed in St. Petersburg in 1903 to 1907 in which he witnessed the Russian Revolution of 1905 and the Russo-Japanese War.

[1][3] During the First World War, Nadolny led a political section of the German General Staff, the so-called Sektion Politik Berlin des Generalstabs.

[4][5] In 1915, Nadolny shipped cultures of anthrax and glanders, a horse disease that is also deadly to humans, to the German embassy in Romania to use them to target animals traded with the Russian Empire.

[14] Ultimately, Neurath was chosen by Schleicher to be the foreign minister in the "Cabinet of the President's Friends", as the Papen government was known, and he never forgot that Nadolny was disappointed that he did not get the portfolio that he had greatly wanted.

[14] Nadolny's attempts to enhance German–Soviet relations on the basis of the Treaty of Rapallo (1922) were largely unsuccessful as it contradicted Hitler's policy.

Nadolny believed in 1933 that it was feasible for Nazi Germany to annex Polish territories in Pomerania in exchange for promising Lithuanian Memel to the Poles[15] Nadolny argued against the 1934 German–Polish Non-Aggression Pact because of its influence on German–Soviet relations and urged "decent treatment" of Soviet ambassador Maxim Litvinov "even if he is Jewish".

[19] On another occasion, he addressed Hitler as "Herr Reichskanzler", as opposed to the common "Mein Führer", and he refused to use the Nazi salute.

During the Second World War, he served as a captain and later major at the High Command of the Wehrmacht and on the staff of Admiral Wilhelm Canaris.