Federal prosecutors said the suspect had sent details and floor plans of the Bundestag building in Berlin to Russian military intelligence.
A man has been given a two-year suspended prison sentence for passing information on the German parliament to Russia.
The 56-year-old German suspect -- a former employee at a computer security firm -- was convicted of spying for a foreign entity.
Prosecutors said the man had sent details and floor plans of the Bundestag building to Russian military intelligence.
He had allegedly met a military attaché at the Russian embassy in 2017 and handed over a CD containing more than 300 files of blueprints of buildings used by the Bundestag.
Prosecutors say the Russian embassy employee was an officer with the country's GRU military intelligence agency.
The 56-year-old suspect -- identified only as Jens F. -- had pleaded not guilty to the charges.
He was offered the chance to admit to the crime for a prison sentence of between 20 months and 2 years.
His defence lawyers said there was no evidence he had passed on the files and argued that the case was based on the suspect's former work in East Germany.
Relations between Germany and Russia have become tense in recent years, after a number of diplomatic incidents.
Russia has denied allegations that it was behind a large-scale hacking against the Bundestag and Chancellor Angela Merkel's office in 2015.
In June, a Russian scientist working at a Bavarian university was also arrested on suspicion of spying for Moscow.