Waldemar is known as the last in the line of Ascanian margraves starting with Albert the Bear in 1157; he was only succeeded by his minor cousin Henry II, who died one year later.

He was a son of Margrave Conrad of Brandenburg-Stendal and his wife Constance, eldest daughter of the Piast duke Przemysł I of Greater Poland.

Frederick was captured and arrested; to regain his freedom, he had to cede the March of Lusatia as well as the towns of Torgau and Großenhain to Brandenburg and to pay a ransom of 32,000 silver Mark.

In the Imperial election of 1314, Waldemar voted for the Wittelsbach candidate Louis IV against his Habsburg rival Frederick the Fair.

In 1348, an impostor appeared in the Archbishopric of Magdeburg and successfully claimed that he was Waldemar, returning from pilgrimage to the Holy Land after somebody else had been buried in his place.

Quickly gaining support due to the rivalries between the Wittelsbach and Luxembourg dynasties, King Charles IV reinvested him for about two years before "the last Ascanian" was unmasked and fled to the Anhalt court in Dessau, where he spent the rest of his life.