Haeften and his brother Hans Bernd von Haeften were born in Berlin to Hans von Haeften, an army officer and President of the Reichsarchiv. He studied law in his hometown and then worked for a bank in Hamburg until the outbreak of World War II, when he joined the German army.
In 1943, having recovered from a severe wound he had suffered on the eastern front, Haeften became adjutant to Oberstleutnant Claus von Stauffenberg, one of the leading figures in the German Resistance.
On 20 July 1944 Haeften accompanied Stauffenberg to the military high command of the Wehrmacht near Rastenburg, East Prussia, where the latter planted a briefcase bomb in Hitler's Wolfsschanze bunker. After the detonation, Stauffenberg and Haeften rushed to Berlin and, not knowing that Hitler had survived the explosion, engaged in a coup d'état, which would swiftly fail.
On the same day, Haeften, along with Stauffenberg and fellow conspirators General Friedrich Olbricht and Oberst Albrecht Mertz von Quirnheim, was arrested and condemned to death by General Friedrich Fromm. All four were shot after midnight by a ten man firing squad from the Grossdeutschland Guard Battalion in the courtyard of the War Ministry, the Bendlerblock. When Stauffenberg was about to be shot, in a last dramatic gesture of defiance, Haeften threw himself into the path of the bullets.