Dorothea was the eldest child of Elector Frederick II of Brandenburg (1413–1471) from his marriage to Catherine (1421–1476), daughter of Elector Frederick I of Saxony.
She married on 12 February 1464 in Lüneburg Duke John V of Saxe-Lauenburg (1439–1507). As she was oldest daughter of the Elector Frederick, who had no surviving sons, the marriage agreement was important. In addition to a 10000florins dowry, Frederick promised his son-in-law everything that he could legally leave to his daughter. Later, however, Frederick abdicated in favour of his younger brother Albert Achilles, so as to keep his possessions in the family.
Frederick also failed to pay the dowry to his son-in-law. This led Dorothea's uncle John the Alchemist to compare himself with the Elector Frederick in 1482.
^Adolph Friedrich Riedel: Codex diplomaticus Brandenburgensis: Sammlung der Urkunden, Chroniken und sonstigen Quellenschriften für die Geschichte der Mark Brandenburg und ihrer Regenten, vol. 6, F. H. Morin, 1865, p. 121