The lawyer pleaded not guilty at the trial held behind closed doors.
The lawyer, a man with dual citizenship identified only as Stanislaw Sz. for legal reasons, pleaded not guilty at the trial held behind closed doors. He can appeal the verdict.
Judge Agnieszka Domanska said the man gave Russia information on Poland's energy sector, in particular regarding a new liquefied natural gas terminal at Swinoujscie on the Baltic coast, according to the Polish news agency PAP.
He notably got hold of a secret report by the national audit chamber NIK on natural gas contracts and the launch last June of the Swinoujscie terminal, which Poland built to ease its dependence on Russian gas.
Poland currently relies on Russia for about forty percent of its gas, with a third coming from domestic sources and 20 percent from central Asia.
Stanislaw Sz. was arrested in October 2014, at the same time as a Polish officer, Zbigniew J., who was sentenced last year to six years in prison by the Warsaw military court for spying for Russia.
Their cases were related but the two men did not work together, according to Polish media reports.