Dedo I was involved in the rebellion of Duke Henry II of Bavaria against the Holy Roman Emperor Otto II and later against his son Otto III, until June 985, when the Bavarian Duke was finally subjugated in Frankfurt.
In 976, Dedo commanded a Bohemian army, conquered the March of Zeitz, and robbed the Bishop's Church.
Dedo apparently had a good relationship with Archbishop Giselher of Magdeburg, who helped him gain comital rights in the northern Hassegau.
Bishop Thietmar of Merseburg, Lothair's nephew, tells in his chronicle that Dedo I was involved in the devastation of the castle of Wolmirstedt which was in the possession of the Counts of Walbeck.
Dedo was killed by Werner on 13 November 1009 along with his vassals near Mose at the confluence of the Tange and Elbe rivers.