The Moscow city court found Polish citizen Marian Radzajewski guilty of Article 276 of the Russian Criminal Code, espionage, the court's press service stated.
"He was sentenced to imprisonment for a term of 14 years in a strict regime colony", the press service added.
The trial was conducted in a closed session, since its materials contain information constituting state secrets.
According to the Russian Security Service (FSB), Radzajewski tried to obtain secret parts of the S-300 anti-aircraft missile system. When trying to make a deal, he was detained red-handed.
Radzajewski reportedly acted in the interests of a Polish organisation, the leading supplier for Poland's national armed forces and special services.
In March, Russian President Vladimir Putin stated Russia's special services intercepted almost 600 foreign intelligence officers and agents last year.
The S-300 is a Russian long-range surface-to-air missile system, developed to defend against aircraft and cruise missiles. The system is capable of hitting even the smallest aerial objects as well as cruise missiles. Different variations of the S-300 are possessed by nearly 14 countries, mainly in Eastern Europe, including Slovakia.