From 1939, Jaeger forged contacts with resistance elements within the Wehrmacht, including Hans Oster, Friedrich Olbricht and Ludwig Beck.
After his wife's death during a British bombing raid on 17 February 1942, Jaeger spoke with his son for the first time about his contacts with the resistance and their plans to overthrow Adolf Hitler.
[citation needed] On 20 July 1944, the day of the attempt on Hitler's life, Jaeger was commander of the Panzer reserve troops in defence districts II (Stettin) and XXI (Kalisch).
After the briefcase bomb exploded at the Wolf's Lair in East Prussia, Jaeger received orders from Claus Schenk von Stauffenberg to arrest an SS Oberführer.
On 21 August, Friedrich Gustav Jaeger was sentenced to death for treason by Roland Freisler at the Volksgerichtshof, and he was hanged later the same day at Plötzensee Prison in Berlin.