His parents, Adalbert and Ida Hahn, were both involved in the porcelain industry.
The Hahns moved to Rudolstadt where Hermann was meant to attend Gymnasium, but he left school in order to study drawing under the Hofmaler Rudolf Oppenheim.
He then trained in sculpting wood and in 1887 began his studies in Munich, at the Kunstgewerbeschule and the Akademie der Bildenden Künste.
He formed deep ties to Munich and the Akademie, eventually becoming a professor himself and teaching there for decades.
Hahn traveled abroad throughout Europe and was especially influenced by the sculpture of antiquity.