In 1901, he founded the Deutsch-Luxemburgische Bergwerks- und Hütten-AG together with Hugo Stinnes, which became one of the largest companies in its field.
In September 1906 the German Chancellor, Bernhard von Bülow, appointed Dernburg as director of the Colonial Section of the Foreign Office.
Dernburg campaigned for a policy of rational economic development of the colonies, based upon the construction of railways.
Here the reforming governor, Albrecht von Rechenberg, organised a carefully choreographed programme which convinced Dernburg that the future of the colony lay in the promotion of African small-holder agriculture, rather than large European-owned plantations.
Late in 1909 he went to the United States, to investigate the possibilities of improving cotton production in the German colonies.
[5] From 17 April to 20 June 1919, he served in the cabinet of Philipp Scheidemann as Federal Minister of Finance and Vice Chancellor.