Thietmar witnessed the struggles of the young Ottonian king Otto III and his mother Theophanu to secure their reign. He took some part in some political events of the time; in 994 he was a hostage in the hands of the Norsemen, and he was not unfamiliar with the actualities of war. Upon the death of his parents, he inherited large parts of the Walbeck estates and in 1002 became provost of the family monastery, established by his grandfather Count Lothair II. On 21 December 1004, he was ordained as a priest by Archbishop Tagino of Magdeburg.