After attending the Lübeck Gymnasium, he studied jurisprudence at the universities of Bonn, Berlin, and Göttingen and completed his professional training by a long stay abroad, particularly Paris.

Krüger's efficiency was fully acknowledged and in 1850 the city sent him as its representative to the Erfurt Union and the following year to the Elbe Ship Navigation commission in Magdeburg.

[1] In 1855 he became the Minister-Resident of the Hanseatic states at Copenhagen and conducted negotiations which resulted in the abolition of the Sound Dues, which had been a tax on Lübeck’s trade out from the Baltic to the open sea.

Already in Copenhagen, he had successfully represented Hamburg's interest in the construction of a railway connecting this town to Altona (in Holstein) and concluded an agreement with the Danish government in 1860.

[2] All three Hanseatic cities, through their envoy Krüger, voted against the Austrian proposal in the Bundestag on 14 June and jointly put a declaration formulated by Lübeck reasoning that the events in Holstein did not give rise to the mobilisation of the Confederation because the danger of an immediate collision was eliminated.

The Lübeck Senate sided with the Prussian view that the Confederation should no longer exist, because of the illegal action of mobilisation and proposed that their Bundestag envoy Krüger be recalled.

The Prussian ambassador to the Hanseatic states, Emil von Richthofen, who also took part in this conference, emphasised that the abolition of all relations with Prussia's opponents was indispensable as a sign of friendly neutrality, and that therefore their Bundestag envoy in Frankfurt, Krüger, must be recalled.

[3] Richthofen now tried to persuade the Senate of Hamburg to give in to other demands, namely to send a military contingent to assist Prussia and to agree to a new close federation under Prussian hegemony.

[1] In addition to his role as Hanseatic envoy in Berlin, he was appointed Lübeck’s plenipotentiary to the new Federal Council in 1868, alongside Gustav Kirchenpauer who represented Hamburg.

In the Federal Council, Kruger contributed to the Judicial Committee, maritime affairs, trade and transport, railway, post and telegraphs, Alsace-Lorraine and the construction of the Reichstag building.

On 25 May 1881 this agreement was signed between the Prussian Finance Minister Karl Bitter and the State Secretary of the imperial Treasury, on the one hand, Hamburg's Plenipotentiary Senators Johannes Versmann and William Henry O'Swald, and Krüger, on the other.