From 31 January 1512, he was canon of Halberstadt in the service of the Brandenburg Elector Joachim I on various diplomatic missions.
On 12 March 1513, he witnessed a comparison between Duke Heinrich I of Brunswick and Lüneburg and Count Johann von Holstein-Schaumburg.
In the spring of 1519, Dietrich von Hardenberg served twice as an envoy in the service of Elector Joachim I in Cologne, where he was to sound out the political position of Archbishop Hermann V and win him over for the election of King Franz I as emperor.
At the end of 1520, he went to the French court on a diplomatic mission together with the provost of Besskow, Andreas Huth.
As bishop he proved himself to be a zealous Catholic and an enemy of the Reformation, which, however, gained a lot of ground under his episcopacy as a result of careless measures, especially in the parts of the Brandenburg diocese outside of the Kurmark territory.