As a member of the German-Liberal Party, Karl represented the landed nobility in the Bohemian Landtag (provincial assembly) during the 1840s and took a conspicuous part in defending the constitutional system against Prince Metternich's Vormärz regime, which was becoming increasingly unpopluar throughout the Austrian Empire and ultimately culminated in the German revolutions of 1848–1849.

On the advent of the new constitutional era in 1861, Franz Joseph I established a bicameral Imperial Council in the Austrian Empire and appointed Karl as the first President of the House of Lords.

In 1861 Karl also rejoined the Bohemian Landtag where he served intermittently as Oberstlandmarschall (supreme provincial marshal) of Bohemia and as chairman of the Landesausschuss (state committee) until 1883.

[3] After the constitutional changes that led to the creation the dual monarchy of Austria-Hungary in 1867, the Emperor turned to the German-Liberals (who had supported the Austro-Hungarian Compromise) to form the new Austrian government and appointed Karl as the first Prime Minister.

In his view, Viscount Taaffe and Foreign Minister Count Friedrich Ferdinand von Beust made excessive concessions to the Czech National Party.