 From 19 March 1848 he acted as the first Prussian Minister President and Foreign Minister, however, he again resigned within a few days, after the king chose to place himself at the head of the revolutionary movement.A member of the Provincial Brandenburg "Landtag" assembly since 1839, Arnim from 18 May to 10 June 1848 was a representative for Prenzlau in the Frankfurt Parliament and also was a member of the short-lived Erfurt Union Parliament in 1850.He belonged to the newly established Prussian House of Representatives from 1849 and later joined the House of Lords chamber of the Prussian Prliament.