The suspect named as Jens F., 56, was found guilty of handing over a CD with more than 300 files of floor plans of buildings used by the German Bundestag to the military attache of the Russian embassy in 2017.
The military attache in post at that time is suspected to have been an employee of Russia’s GRU military intelligence service. The suspect meanwhile worked for a security company contracted by the Bundestag.
According to media reports, Jens F. was previously an officer in a tank division of the East German army and had also worked informally for the feared Stasi secret police.
Prosecutors had demanded a sentence of two years and nine months, while the defence had argued he should be acquitted because there was no proof he had transmitted the information to the Russians.
Jens F.’s lawyer Friedrich Humke said prosecutors had built their case purely on his client’s past and his activities in the former communist East Germany.
The case comes at a time of particularly rocky ties between Berlin and Moscow over a series of espionage cases, as well as the poisoning and jailing of Kremlin critic Alexei Navalny.
In June, German police arrested a Russian scientist working at a university in the southern city of Augsburg, accusing him of spying for Moscow.
Germany has also repeatedly accused Russia of cyberattacks on its soil.
The most high-profile incident blamed on Russian hackers to date was a cyberattack in 2015 that completely paralysed the computer network of the Bundestag lower house of parliament, forcing the entire institution offline for days while it was fixed.
In another case before a German court, a Russian man is on trial over the assassination of a former Chechen commander in a Berlin park, allegedly on Russia’s orders.
Moscow has denied being behind such actions.