German police seized the British national, named David S., in Potsdam, near Berlin.
It followed a joint investigation by German and UK authorities.
Germany’s Federal Criminal Police Office conducted the arrest.
The suspect’s home and workplace have also been searched by police.
He is accused of having worked for the Russian secret service since at least November 2020.
During this time the suspect allegedly handed over secret material, which he came across via his work, at least once.
In return he “received cash in an as yet unknown amount”.
In a statement German police said: “David S. was employed as a local staff member at the British Embassy in Berlin until his arrest.
“On at least one occasion, he transmitted documents he had obtained in the course of his professional duties to a representative of a Russian intelligence service.
“The defendant received cash in an as yet unknown amount in return for his information transfer.
“The arrest is the result of joint investigations by German and British authorities.
“The suspect will be brough before the investigating judge of the Federal Supreme Court later today (August 11, 2021), who will open the arrest warrant for him and decide on the execution of pre-trial detention.”
Russia has been accused of mounting a sophisticated espionage operation against western powers.
Additional reporting by Monika Pallenberg.
More to follow…