He was the fourth son of the Landgrave Maurice of Hesse-Kassel and his second wife Juliane of Nassau-Siegen.
They had one daughter: In Weimar on 2 February 1642 Herman married secondly Princess Kunigunde Juliane of Anhalt-Dessau (b. Dessau, 17 February 1608 - d. Rotenburg, 26 September 1683), daughter of John George I, Prince of Anhalt-Dessau.
Herman suffered all his life from a crippled foot and had to wear iron braces to support his leg.
His treatise Beiläufige Cosmographische Beschreibung des Niederfürstentums Hessen of 1641 is among the standard works of 17th century Hessian geography.
In 1651, Herman built a new school, at his own expense, at the address Löbergasse 2, as indicated by an inscription on the building.