Hewel was born in 1904 to parents Anton and Elsa in Cologne, where his father ran a cocoa factory. His father died in 1913, leaving Elsa to run the factory. Although still a teenager at the time, Hewel was one of the earliest members of the Nazi Party, and is calculated to have been between the 200th and 300th person to actually join the group. Hewel graduated in 1923 and attended the Technical University of Munich. The same year, he took part in the Nazi's failed Beer Hall Putsch. After Hitler's subsequent conviction for treason, Hewel stayed in Landsberg prison with him and, for several months, acted as Hitler's valet.