The arrest follows a joint investigation by German and British law enforcement.
The man was employed as a local staff member at the embassy until his arrest in Potsdam, on suspicion of having forwarded information to the Russian intelligence service since November 2020.
Police also searched the man’s home and workplace after they arrested him.
His arrest warrant said that “on at least one occasion he forwarded documents obtained in the course of his professional activity to a representative of a Russian intelligence service.”
The German Federal Prosecutors Office added, “The defendant received cash in an as yet unknown amount in return for his information transfer.”
German Foreign Minister Heiko Maas said the alleged spying is “absolutely unacceptable,” and expressed the country’s “full solidarity” with the UK.
The man was brought before Germany’s Federal Court of Justice in Karlsruhe on Wednesday to decide on pre-trial detention, and was ordered to remain under arrest pending further inquiries.
The man reportedly provided the Russians with documents containing information on counterterrorism, according to German online magazine Focus Online.
Security specialist Edward Lucas told Times Radio that the arrest was “a reminder of how much effort the Russians put in to trying to find out what Western alliances are up to.”
Germany has seen two other arrests of alleged spying for Russia this year.
In June, a Russian scientist at a German university was accused of working for Russia’s secret service since October 2020.
In February, a German man was accused of having passed the floor plans of the German federal parliament to Russian secret services.