In 1749 he entered the Dutch States Army as field marshal by request of William IV, for twenty thousand guilders per annum, although he also retained his position as an Austrian field-marshal and Protestant Generalfeldzeugmeister of the Holy Roman Empire.
 William's wife Anne was initially sceptical about his appointment and opposed it.

In 1751 he became the governor of the garrison city of Bois-le-Duc, where the stadholder had had particular influence since 1629.
 After the death of William IV on 22 October 1751 and Anne's appointment as regent, Louis Ernest was appointed captain-general (commander-in-chief) of the Netherlands, reorganising the higher strata of the army.
 Britain and Prussia asked him to command the allied armies in the Seven Years' War, but Louis Ernest refused out of respect for the Dutch Republic's neutrality.
His brother Duke Ferdinand was given command of the Anglo-German army in Hanover in 1757.
In 1759 Louis was used as an intermediary in an attempt to mediate the conflict, but plans for a peace congress came to nothing.

From the death of William V's mother Anne in 1759 to William's majority in 1766, he was William's guardian and led the Netherlands' state affairs in his name.
 The prince called Louis Ernest his second father, but the Frisian nobility under Onno Zwier van Haren opposed Louis Ernest.
 Simultaneously, Louis Ernest began reforming the stadholder system that had previously appointed qualified persons to the regions in reward for their loyalty.
 Such favorites had been supposed to take care of local disputes independently.
 As a result, there was no efficient administrative device in the Republic, nor an equitable apportioning of offices.
 The prince, losing himself in the details, made it known that he valued advice, which, however, he usually sent back by return of post without any alterations.
 For over a dozen years he had been drilled by Brunswick and Fagel to believe that his only job was to sign the documents they placed in front of him (and judging from his signature, he was not very good at that).
In 1749 he entered the Dutch States Army as field marshal by request of William IV, for twenty thousand guilders per annum, although he also retained his position as an Austrian field-marshal and Protestant Generalfeldzeugmeister of the Holy Roman Empire.  William's wife Anne was initially sceptical about his appointment and opposed it.
In 1751 he became the governor of the garrison city of Bois-le-Duc, where the stadholder had had particular influence since 1629.  After the death of William IV on 22 October 1751 and Anne's appointment as regent, Louis Ernest was appointed captain-general (commander-in-chief) of the Netherlands, reorganising the higher strata of the army.  Britain and Prussia asked him to command the allied armies in the Seven Years' War, but Louis Ernest refused out of respect for the Dutch Republic's neutrality. His brother Duke Ferdinand was given command of the Anglo-German army in Hanover in 1757. In 1759 Louis was used as an intermediary in an attempt to mediate the conflict, but plans for a peace congress came to nothing.
From the death of William V's mother Anne in 1759 to William's majority in 1766, he was William's guardian and led the Netherlands' state affairs in his name.  The prince called Louis Ernest his second father, but the Frisian nobility under Onno Zwier van Haren opposed Louis Ernest.  Simultaneously, Louis Ernest began reforming the stadholder system that had previously appointed qualified persons to the regions in reward for their loyalty.  Such favorites had been supposed to take care of local disputes independently.  As a result, there was no efficient administrative device in the Republic, nor an equitable apportioning of offices.  The prince, losing himself in the details, made it known that he valued advice, which, however, he usually sent back by return of post without any alterations.  For over a dozen years he had been drilled by Brunswick and Fagel to believe that his only job was to sign the documents they placed in front of him (and judging from his signature, he was not very good at that).
Duke Louis Ernest of Brunswick-Lüneburg