Adlene Hicheur was arrested in 2009 after police intercepted his emails to an alleged contact in al-Qaeda.
The emails suggested Algerian-born Adlene Hicheur was willing to be part of an “active terrorist unit”, attacking targets in France.
Defense lawyers argued that their client had never been part of a plot.
Adlene Hicheur, who is a particle physicist, worked as a researcher studying the origins of the universe at CERN.
His father embraced him in the Paris courtroom before he was taken away to prison.
Adlene Hicheur, 35, has already spent two and a half years in jail while awaiting trial.
He came under suspicion when threatening messages were sent to President Nicolas Sarkozy in early 2008.
The security services uncovered a series of email exchanges between Adlene Hicheur and an alleged al-Qaeda member called Mustapha Debchi.
After his arrest in 2009 police found a large quantity of Islamist literature at his parents’ home.
At the start of his trial the scientist admitted that he had been going through a psychologically “turbulent” time in his life when he wrote the emails.
Adlene Hicheur had suffered a serious back injury, for which he had been taking morphine.
But he always denied he intended to carry out any attacks.
His lawyer, Patrick Baudouin, described the verdict as “scandalous”.
“Everything has been done to demonize him,” he said.
Adlene Hicheur has not yet decided whether or not to appeal.
If he decides not to, with time off for good behavior, he should be released soon, Patrick Baudouin said.
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