Gunzelin aided Henry the Lion in his campaign against the Obotrites.[2]: 8 After Gunzelin distinguished himself in this campaign, Henry installed him as Burgrave of the castles of Schwerin and Ilow.[2]: 8
In 1164 Gunzelin defended the castles of Ilow and Schwerin against the army of Pribislaw. He participated in the Battle of Verchen during this campaign.[2]: 8 When the Obotrite lands were restored to Pribislaw in 1167 as a vassal of Duke Henry, Schwerin and a large surrounding area were separated and retained by Gunzelin as Count.[2]: 8
The Christianization of the newly conquered lands was accomplished by Bishop Berno under Gunzelin's protection.[1] Gunzelin restricted the rights of the Slavic population in the County of Schwerin, and brought settlers from Germany into his new lands.[3]: 229
Gunzelin seems to have been a true friend of Duke Henry.[2]: 1 In 1172 he accompanied Henry on a pilgrimage to Jerusalem.[2]: 1 Gunzelin supported Henry in his war against Emperor Frederick Barbarossa from 1180 to 1181, after which most of Henry's lands were stripped from him.[1] Gunzelin opposed his new overlord, Bernhard, who had been appointed Duke of Saxony by the Emperor after Henry's dispossession.[1]
Gunzelin died on June 18, 1185, and was buried in Schwerin Cathedral.[2]: 8–9 Gunzelin's sons Helmold, Gunzelin, and Henry all ruled as Count of Schwerin, with Gunzelin II and Henry ruling jointly.[3]: 230 His son Hermann was a rival claimant to Brunward, the second Bishop of Schwerin.[1] His youngest son Frederick succeeded Brunward as the third Bishop of Schwerin.[1][3]: 237
