Thousands of people turned out at the airport to greet him on his arrival from London.
His return is another visible symbol of the change that has swept Tunisia since President Zine al-Abidine Ben Ali was ousted by popular protests earlier this month.
Ghannouchi's return has fanned fears that he will weaken the secular system enforced in Tunisia since its independence from France in 1956. But in his first interview after returning to Tunisia, Ghannouchi told the Associated Press that Western media have tried to portray him like “Khomeini, but that's not me.”
Ghannouchi is the head of Tunisia's main Islamist movement Ennahda, which was banned by President Ben Ali after 1989 elections in which Ennahda officially won 17 percent of the vote, second only to the ruling party.
The ousted president had branded Ennahda an extremist group. Experts on Islamic movements say the group's ideology is more moderate than that of the Muslim Brotherhood in Egypt.