Speaking at a meeting in Washington, Ghannouchi said that Saudi officials will face a revolution unless they give in to the demands of the youth.
Riyadh needs to surrender to the people's will and hand over power to the nation, he added.
Saudi Arabia has been swept with unrest over the past months in the face of the monarchy's known intolerance of dissent.
Meanwhile, the Tunisian official said his movement's stance regarding Israel will remain hostile.
He also supported the Palestinian resistance movement of Hamas in its fight against Israel and said Tunisia would not recognize the US-backed two-state solution.
In October, the al-Nahda party won the majority of the seats in the assembly months after Tunisians overthrew the US-backed despotic regime of Zine El Abidine Ben Ali in a popular uprising.
Tunisians held massive street protests that eventually toppled Ben Ali after 23 years in power. Ben Ali fled to Saudi Arabia as the Tunisian revolution was gaining momentum.