An appeals court in Antwerp, northern Belgium, stripped on Tuesday Fouad Belkacem, who is of Moroccan origin, of his nationality after he was found guilty of recruiting militants.
Belkacem's lawyer Liliane Verjauw denounced the court’s decision, saying she would take further action to restore his nationality.
She warned that his whole family would suffer if he was deported to Morocco.
Belgium's immigration minister Theo Francken, who belongs to the Flemish nationalist N-VA party, welcomed the court's decision.
"This should happen automatically for terrorism convictions," he said.
He recalled a draft-law sponsored by a fellow N-VA politician supported automatically stripping citizenship for any Belgian who holds another nationality and is convicted of terrorism.
Belkacem, a 36-year-old born in Belgium to Moroccan parents, was sentenced in 2015 to 12 years in prison for heading Sharia4Belgium.
In September, the appeals court heard the closing statements of the prosecution and the defense.
According to the prosecution, Belkacem intended to stay in Belgium to spread his extremist thoughts. But his defense team stressed that the man no longer poses a threat and that he had regretted his previous activities.
At the time, Belgium media quoted Verjauw as saying that the suspect told the court that he intended no harm by establishing Sharia4Belgium and that things had gone out of control.
He also hoped that the court would not deport him.
