In April 1144 Duke Ulrich I died, Herman's elder brother Henry V succeeded him. He married Elizabeth, a daughter of Margrave Leopold of Styria, and died childless on 12 October 1161, whereafter Herman succeeded him as Carinthian duke.[1]
With varying degrees of success he tried to consolidate his position in Carinthia by achieving the office of a Vogt protector over the Diocese of Gurk as well as over the Carinthian possessions of the Bishopric of Bamberg and the Patriarchate of Aquileia. Like his brother, he was stuck in territorial disputes with the Otakar margraves of Styria and local nobles like the counts of Heunburg and Ortenburg. Upon the death of his uncle Margrave Engelbert III of Istria in 1173, Herman could not assume the margravial title, but inherited his personal possessions around the town of Sankt Veit which emerged as ducal residence.
Herman was the first Sponheim duke to be buried in St. Paul's Abbey in the Lavanttal, established by his great-grandfather Count Engelbert of Spanheim in 1091. He was succeeded by his eldest son Ulrich II.[1]
