Arnim was born on April 4th 1889 and joined the German Army on April 1st 1908. After training he joined the 4th Regiment of Prussian Foot Guards and served as a junior officer during World War One. Arnim decided to stay in the army after the war ended.
In January 1938, Arnim was promoted to major general and was given the command of the 4th Frontier Zone in February in the same year.
When Germany launched its attack on Poland on September 1st 1939, Arnim commanded the 52nd Infantry Division. On December 1st he was promoted to lieutenant general. Arnim participated in the attack on Western Europe and after this was given command of the 17th Panzer Division in October 1940.
This unit formed part of Army Group Centre for ‘Operation Barbarossa’. The first stage of this massive attack on the Soviet Union was very successful and Hitler rewarded his senior commanders for this success. Arnim was promoted to general in October 1941 and given command of the XXXIX Panzer Corps in November 1941.
Unlike many other senior army commanders who were to remain on the Eastern Front, Arnim was sent to North Africa to bolster the Axis units there. Promoted to colonel general, Arnim was given the command of the 5th Panzer Army in December 1942. When Erwin Rommel returned to Europe, Arnim was given command of Army Group Africa (March 1943). However, this promotion came towards the end of the North African campaign and Arnim could do little to withstand the advance of the British 1st and 8th Armies. He surrendered his forces on May 12th 1943 and spent the rest of the war in captivity.