Prosecutors say the man wanted to present himself as a "security expert" to senior Russian military officials.
A German reserve soldier has been convicted of spying for Russian intelligence agencies for several years.
The 65-year-old Bundeswehr reserve officer was found guilty of passing documents and information to Moscow between 2014 and 2020.
Prosecutors say he was in contact with Russia's GRU military intelligence and embassy personnel.
The reservist allegedly passed on information about Germany's economy, including the controversial Nord Stream 2 gas pipeline and the impact of sanctions on Russia after it annexed Crimea in 2014.
"He also provided publications on the security and defense policy of the United States and its Western allies," the Düsseldorf court said.
"The contacts took place partly in person or by telephone, but mainly by e-mail," it added.
"[In exchange] he received invitations to events organised by the Russian embassy in Berlin and to the annual security conference in Moscow."
Prosecutors say the reserve officer held pro-Russian attitudes and wanted to present himself as a "security expert" to senior Russian military officials.
The 65-year-old -- who was arrested in 2020 -- pleaded guilty to the charges. He was handed a suspended prison sentence of one year and nine months.
Relations between Berlin and Moscow have soured in recent years after a series of espionage allegations.
In April, a Russian researcher based in Augsburg was given a suspended sentence for spying on the European Ariane space programme.
In October 2021, a German court also convicted a former IT worker for passing data on the German parliament to Russia.