Siegfried is first mentioned as an ally of Odo I, Margrave of the Saxon Ostmark, in his conflict with Mieszko I, Duke of Poland.
As an interesting sidebar, Mieszko married Oda of Haldensleben, daughter of Dietrich, Margrave of the Nordmark, who was the predecessor of Siegfried’s brother Lothar I as margrave.
In 979, he and his brothers were appointed regents of the County of Möckerngau by Emperor Otto II.
Later that year, he fought with the Saxon army against the Great Slav Rising revolt against the empire.
He supported the Empress Theophanu in her war against Boleslaus II in 990, and while moving against the rebellious Lutici, he fell from his horse and died on 15 March 990.