Bourki Bouchta was picked up from his home in the northern city of Turin early on Tuesday and put on a plane bound for Morocco at Milan's Malpensa airport, the Interior Ministry said in a statement.
The statement said authorities were considering taking similar measures against other foreigners in Italy.
The ministry said Bouchta was expelled after anti-terrorism officials verified that he was responsible for "a serious disturbance of public order" and represented "a danger for the security of the state".
Officials at the ministry declined to discuss specific incidents that might have led to the preacher's deportation.
Some Italian politicians had called for Bouchta's expulsion in 2001, after he defended Osama bin Ladin and publicly condemned the US attacks on Afghanistan.
In 2003, Italy deported imam Abd al-Qadir Fall Mamour back to his native Senegal after he declared that Italians in Afghanistan and Iraq were courting attack as allies of the United States.
At the time, Bouchta spoke out strongly against the expulsion, saying that the government had punished the preacher for his opinions.
Since then, Italy has expelled three other Muslim preachers, including the imam of Rome's main mosque who was deported to his native Algeria in 2004.
The ministry said he had incited violence against Israel and called for the destruction of Islam's enemies.
Bouchta first made headlines in Italy in 1999, when he led thousands of Muslims in Turin in a march to demand that women be allowed to wear headscarves in photos for official identity documents.
A frequent subject of interviews and a guest on TV talk shows, Bouchta - who also owns a halal butchers shop in Turin - is one of the better known faces of the nation's 1.1 million Muslims.
Although known for his often radical pronouncements, he also voiced an appeal in 2004 for the freedom of three Italian hostages kidnapped in Iraq.
The imam's brother, Abd al-Rahman Bouchta, planned to appeal the expulsion decree, the ANSA news agency reported.