Justus Gruner was born as a son of a lawyer in Osnabrück and studied law and political science at the universities of Halle and Göttingen.
Gruner became known as a careful and hard-working civil servant in the areas Prussia had recently conquered in Poland.
He was just a couple of months in the business of spying when he was captured by the police force that worked for Clemens von Metternich, in that time an ally of Imperial France.
His service would be responsible for assisting and keeping an eye on the French administration of the Restoration and for ensuring the safety of the occopying forces of the Allies.
[4] The first success of Gruner and his force in France was the arrest of the French Napoleonic spy Karl Schulmeister.