1290, the first wife of Gerhard II of Holstein-Plön), the eldest daughter of King Valdemar of Sweden and Queen Sophia, who herself was the eldest daughter of King Eric IV of Denmark and his wife Jutta of Saxony who had no male descendants.

Dietrich succeeded his father as head of the House of Oldenburg in 1403, and is patrilineal 14x great-grandfather of King Charles III of the United Kingdom.

During his childhood, Dietrich married a distant cousin, the Countess Adelheid of Oldenburg-Delmenhorst, daughter of Oldenburg Count Otto IV of Delmenhorst, for reasons of succession and uniting the hereditary fiefs.

In 1423, Dietrich married again, to Hedvig of Holstein (born between 1398–1400 and died in 1436), widow of Prince Balthasar of Mecklenburg and daughter of the murdered Duke Gerhard VI of Schleswig and Holstein and his wife Elisabeth of Brunswick and, thus, sister of the reigning Duke Adolf VIII.

Dietrich of Oldenburg is said to have been a rival claimant to the crowns of Sweden and Denmark during the reign of Eric VII/Eric XIII, whose succession was through Christopher I of Denmark, the younger brother of the murdered Eric IV, and through Magnus I of Sweden, younger brother of the deposed King Valdemar.