In 1848, when Prussia made war on Denmark, Lauenburg was occupied at her own request by some Hanoverian troops, and was then administered for three years under the authority of the German confederation, being restored to Denmark in 1851.
In 1823 he had been made secretary of the archives, and in 1827 principal keeper of the royal library at Hanover; from 1832 to 1837 he edited the Hannoverische Zeitung, and more than once sat as a representative in the Hanoverian second chamber.
He was descended from an old Hanoverian family, his father, Karl von Bennigsen, being an officer in the Hanoverian army, who rose to the rank of general and also held diplomatic appointments.
Bennigsen, having studied at the university of Gottingen, entered the Hanoverian civil service.
He was a zealous Hanoverian, and a favourite with Queen Anne in spite of his Whiggism.