He was a paternal uncle of the chronicler Bishop Thietmar of Merseburg, son of his younger brother Siegfried.
After Count Dietrich of Haldensleben in 983 had been deposed from the Northern March for failing to defend the bishoprics of Brandenburg and Havelberg east of the Elbe river in the Great Slav Rising, he was replaced by Lothair, who was first mentioned as margrave in 993.
However, his attempts to wrest the eastern territories of the Northern March from the Slavic Lutici were unsuccessful and he actually ruled only over a small strip of land along the Elbe in the southwest.
He therefore put up resistance against Eckard's candidacy for the succession of late Emperor Otto III in 1002 and won the Saxon nobles over for the support of rivaling Duke Henry IV of Bavaria.
His widow, Godila of Rothenburg, remained unmarried for four years after his death, eventually marrying Herman II, Count of Werl.