Krockow had been a corporal since 1728 in the infantry regiment "von Holstein" of the Prussian army. On the recommendation of the Polish king Stanislaus I, he entered French service in 1735 and rose there to colonel of the cavalry. His repeated requests for re-establishment in the Prussian service were not fulfilled until March 1757 by King Frederick, although Krockow was granted a patent of 1 May 1748, as colonel and general adjutant. After the death of the major general Christian Friedrich von Blanckensee, Krockow received his place as head of Blanckensee's former dragoon regiment. During the Seven Years' War, he became lieutenant general. He took part in the battles near Prague, Kolin, Hochkirch, Liegnitz and Torgau. He was wounded at Leuthen. He remained in active service until April 1760.