In July 1848 he replaced Heinrich Alexander von Arnim as Foreign Minister, thus joining the government of Gottfried Ludolf Camphausen.

In May 1849 he negotiated the peace treaty with Denmark, and in July 1849 once again took up the position of Foreign Minister in the government of Friedrich Wilhelm, Count Brandenburg.

However, since his German patriotic views were not compatible with the way Prussian politics was developing, he retired from public service on 26 September 1850 as a Wirklicher Geheimer Rat, and from then lived near Koblenz in close contact with the court of the Prince of Prussia, and at Schloss Gebesee in Thuringia.

The main tenets of his foreign policy were the attempt to form an alliance with Britain and Austria, the maintenance of the balance of power in Europe and a strengthening of Prussia's role in Germany.

On the occasion of the Emperor's and Empress' golden wedding anniversary, Schleinitz and his wife were elevated to the rank of Graf (Count) on 11 June 1879.