He served as regent of the Principality of Rügen during the many absences of his older brother, Vitslav II.
[1] In 1268, he issued a charter as prince to Neuenkamp Abbey.
[2] Jaromar acted as regent when his brother went on a crusade to Livonia in 1282.
In this capacity, he issued a privilege of confirmation to Eldena Abbey on 6 July 1282.
Vitslav intended to carve out a principality for his brother in the east to serve as a bulwark against the Teutonic Order, but Jaromar died later that year before the plan came to fruition.