A former Polish chemistry professor has been sentenced to 13 years in prison over a plot to detonate parliament with a massive car-load of explosives.

A Polish court on Monday found Brunon Kwiecien, 48, guilty of planning to assassinate the president, prime minister and lawmakers in an attack on parliament in 2012, of trying to encourage two students to carry out the raid and of illegal weapons possession.

The former professor at Krakow's University of Agriculture in southern Poland had concealed four tons of explosive materials in a car that he planned to use during a parliamentary debate to be attended by then-President Bronislaw Komorowski among others.

Kwiecien was arrested in November 2012 and was found to be in possession of TNT, gunpowder and other explosives as well as firearms, military helmets, bullet-proof vests and fake drivers' licenses.

"If Brunon Kwiecien hadn't been stopped, we would be talking amid the ruins of the state today," Judge Aleksandra Almert said when explaining the court's decision.

"All steps taken by Brunon Kwiecien related to the attack on parliament were driven by his wish to lead a revolution, to kill the president, cabinet ministers and lawmakers," Almert added.

Donald Tusk, the then-prime minister and current EU chief, said at that time that Kwiecien "did not conceal his fascination with [Anders Behring] Breivik," the Norwegian extremist who killed 77 people in a bombing and shooting rampage in Norway in July 2011.

Media reports said he had no obvious links to any political groups or extremists, and was not inspired by anyone.

During the trial, Kwiecien insisted he had fallen victim to "provocation" by Polish undercover security officers who had forced him to act, pretending to want involvement in his plot.

The chemist, who has never denied having planned the raid, has the right to appeal the verdict.