Holstein joined the diplomatic service and in 1860 became an attaché at the Prussian embassy in Saint Petersburg under the authority of Otto von Bismarck and later served as a member of the legations at Rio de Janeiro, London, Washington, Florence, and Copenhagen.
Holstein returned to Berlin, where he assumed office as legation secretary in the Auswärtiges Amt in 1876, both an essential and a suspiciously eyed associate of Bismarck, who behind his back called him a "hyena".
His reluctance to emerge into publicity has been ascribed to the part he had played under Bismarck in the Arnim scandal, which had made him powerful enemies; it was, however, possibly due to a shrinking from the responsibility of office.
This is seen by blunders made on the abandonment of the Reinsurance Treaty with Russia in 1890, his Chinese policy, and also of his part in the Moroccan crisis which led to the Algeciras Conference in 1906.
[6] To the last he believed that Germany's position would remain unsafe until an understanding had been arrived at with Britain, and it was this belief that determined his attitude towards the expansion of the Imperial Navy: beside this, he wrote in February 1909, all other questions were of lesser account.
His views on this question were summarized in a memorandum of December 1907, of which Rath gives a résumé: Holstein objected to the programme of Admiral Alfred von Tirpitz and the Navy League on three main grounds: the ill-feeling likely to be aroused in South Germany, the inevitable dislocation of the finances through the huge additional charges involved, and the suspicion of Germany's motives in foreign countries, which would bind Britain still closer to France.