He was called up as a reserve officer on the outbreak of war, transferring to an administrative post (Wirtschaftsstab Ost) assigned to the Armed Forces High Command in Berlin in 1942.
In January 1940, he began to work closely with Helmuth James Graf von Moltke, with whom he initiated and led the discussions of the Kreisau Circle, which met very often at Yorck’s home in Berlin-Lichterfelde.
Yorck, who took part in all three of the circle’s conferences in Kreisau, supported a coup attempt to be launched with an assassination, unlike his friend Moltke.
When Claus Schenk Graf von Stauffenberg began to speed up preparations for the coup in Berlin in September 1943, he and Yorck came into close contact.
After the failed coup attempt, Yorck was arrested in the Bendlerblock in Berlin in the late evening of 20 July 1944, sentenced to death by the People’s Court on 8 August 1944, and executed the same day in Berlin-Plötzensee.