[1] On 17 December 1922, Schlessmann became a member of the Nazi Party (NSDAP) co-founding the Ortsgruppe (Local Group) in Essen and becoming the Deputy Ortsgruppenleiter.

In August 1930, Schlessmann was appointed Deputy Gauleiter in Gau Essen under Josef Terboven but remained in this post only until 31 December.

[3] Schlessmann was named acting Polizeipräsident (Police Chief) in Bochum on 27 October 1933; his appointment was made permanent on 1 April 1934.

At his own request, Schlessmann was relieved of his police post on 31 December 1939 in order to devote himself full-time to his work as a Party official.

[3] Terboven was appointed Reichskommissar for Norway on 24 April 1940, while formally retaining his position as Gauleiter of Essen.

As a large industrial center and the site of the Krupp armaments works, Essen was a frequent target of Allied bombing raids.

[4] After exhorting the populace of Essen to fight to the last man as the Allied forces approached the city, Schlessmann went into hiding with his 24-year-old secretary and mistress, under the alias "Fritz Selig".

In a 1947 court proceeding in Detmold, he was sentenced to five years in prison, which he served until 13 June 1950, when he was released from the Esterwegen internment camp.