Dreikönigsbündnis
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.