The scion of an industrialist, Canaris graduated from secondary school in 1905 and then joined the Imperial Navy. He took part in the First World War, serving as commander of a U-boat from the end of 1917 onward. On his return, taken aback by the November Revolution and the end of the war at sea, Canaris supported the formation of citizens’ militias and naval brigades to suppress the November Revolution. He was an assessor in the military court tasked with ruling on the murders of Rosa Luxemburg and Karl Liebknecht, with the court voting for the acquittal of the perpetrators and helping one of the convicted men to escape. From 1920 onward, he held various positions within the Reichsmarine (navy).
In January 1935, Canaris was appointed head of the Defense Department (Abwehrabteilung), the military secret service within the Reich Defense Ministry, which was subsumed under the Oberkommando of the Wehrmacht (Armed Forces High Command, OKW) as the Foreign/Defense Division in 1938. The Foreign/Defense Division worked effectively in the interests of the Nazi regime: It played a significant part in ensuring the success of the regime's war effort and in the fight against resistance circles abroad. The Geheime Feldpolizei (Secret Field Police), which was heavily involved in the racist war of annihilation, supported the Division. Canaris used the privileged access to information that he had in a variety of ways: Although as head of the secret service he contributed to the fight against 'enemies of the state' on the one hand, he also supported opponents of the Nazi regime on the other, especially within its own ranks. The extent to which Canaris's own ideas chimed with those of the Nazi regime is not always obvious. However, he did protest in writing against the shooting of Russian POWs and explored the chances of a separate peace abroad. He passed on information to resistance activists and protected those being persecuted by helping them to flee abroad. In addition, he covered up the bold activities of overt opponents of Hitler in his office, such as Hans Oster and Hans von Dohnanyi, who were engaged in passing on attack plans to foreign nations.
Canaris was deposed in February 1944 after Oster and von Dohnanyi had already been arrested. Three days after the assassination attempt on July 20, 1944, the Nazis arrested him. He was hanged along with Oster in Flossenbürg Concentration Camp on April 8, 1945.
