He joined the army in 1902 as a Fahnenjunker and, in 1903, was promoted to the rank of second lieutenant in the 1st Posen Field Artillery Regiment Number 20.

In 1910, he was sent to the Military Riding Institute for 2 years where he was promoted to lieutenant and, shortly thereafter, married Margarete Hauffe on 28 August 1911.

In November he was promoted to the rank of captain and, in January 1915, was appointed as adjutant of the 10th Field Artillery Brigade.

[2][1] In 1939, as the Wehrmacht mobilised, Petzel took over the I Army Corps as its commanding general and led it during the Invasion of Poland.

On 1 October 1939 he was promoted to General of Artillery[2] and Commander I Army Corps, but was almost immediately given command of two military districts, Wehrkreis III and Wehrkreis XXI with his headquarters in German occupied city of Posen (today Poznań).