In 1703, he became a
chamberlain at the
Brandenburg-Prussian court. He also served in the
Prussian army and took part in the
Battle of Höchstädt in 1704 where he was wounded. In 1706, he was appointed governor of the Uckermark. In 1710, he managed to pay off the co-heirs of the
Boitzenburger estate, redeem pledged property and become the sole owner of the villages of Kröchlendorff (today part of
Nordwestuckermark),
Milow,
Kuhz,
Wichmannsdorf,
Kleinow and
Falkenwalde. He had a manor built in the
baroque style (Kröchlendorff Castle was later built there). In 1712, Arnim became a secret judicial councilor and, in 1738, King
Frederick William I appointed him president of the
Oberappellationsgericht zu Berlin (later named the Prussian Supreme Tribunal) and the
Ravensberg appeal court in
Berlin. He also became feudal director, real privy councilor and Minister of State and
War. Arnim also took over the Silesian Justice Department in 1743. Because he did not agree with extensive judicial reforms approved by
Frederick II, he resigned in 1748. Afterwards he was director of the Brandenburg landscape. For his services in the civil service he was awarded the
Order of the Black Eagle in December 1749. He was also the resident commander of the
Order of St. John in
Werben. Frederick II brought him back into civil service in 1749 and appointed him directing minister and vice president of the General Directorate. He was also postmaster general and senior curator of the secondary schools. He was one of the most decisive representatives of corporate interests in the General Directorate. At
Boitzenburg Castle he laid the foundations for the castle library and had a side wing built specifically for it. Following the desertion of the surrounding area since the
Thirty Years' War, Arnim brought in settlers as part of the internal colonization, contributing to the revitalization of area. ==Personal life==