File Photo: The main building of the Russian Federal Security Service, former KGB headquarters, in Lubyanka Square in Moscow, Russia, on Jan. 27, 2015. AP
Prosecutors say the suspect, named as Ralph G., was "in contact with a Russian intelligence service through various people" between 2014 and 2020.
They accuse him of sharing information on the inner workings of Germany's military reserve and "civil defence" as well as the impact of sanctions levelled against Moscow in 2014, and the Nord Stream 2 gas pipeline project.
He is also said to have shared the "personal data of high ranking members of the Bundeswehr".
The trial comes at a time when ties between Moscow and Berlin are in tatters over Russia's invasion of Ukraine.
According to Der Spiegel magazine, Ralph G. was a lieutenant colonel in the reserve who also worked as a sales manager for an international engineering company in western Germany.
Thanks to his civilian profession, he "belonged to several German business committees" and was also able to pass on personal information on figures from the business world, according to prosecutors.
He is not thought to have been paid for his services, but instead received "invitations to events organised by the Russian government agencies".
According to Der Spiegel, Ralph G.'s main contacts were two employees of Russia's GRU military intelligence who were accredited as military attaches in Germany.
The information was reportedly passed on through personal meetings, phonecalls, email and WhatsApp.
Most of it came from publicly available sources, but Ralph G. is also accused of sharing excerpts from an official government document on Germany's relationship with Russia following Russia's annexation of Crimea.
String of spies
After his arrest in 2020, Ralph G. admitted to having supplied information to the Russians. However, he claims not to have known that his contacts were working for the GRU, Der Spiegel reported.
Even before Russia's invasion of Ukraine, Berlin and Moscow had been at odds for several years over issues including cyberattacks and several other espionage cases.
Last year, a German court sentenced a Russian man to life in prison for shooting dead a former Chechen commander in a Berlin park in broad daylight, a murder prosecutors say was ordered by Moscow.
A Russian man also went on trial in Munich in June charged with plotting to kill a Chechen dissident living in Germany on the orders of Chechen leader Ramzan Kadyrov.
Ralph G. is the latest in a string of suspected Russian spies uncovered on German soil.
A Munich court in April handed a one-year suspended prison sentence to a Russian scientist for passing on secrets about Europe's Ariane space rocket programme to Moscow while working at a German university.
Days earlier, a security guard at the British embassy in Berlin was extradited to the UK face charges of spying for Russia.
In October 2021, a German man was handed a two-year suspended sentence for passing on floor plans of parliament buildings to Russian secret services while employed by a security company.