Rached Ghannouchi, a former radical preacher, founded the Ennahda, or Awakening, movement in 1981 with intellectuals who were inspired by the Muslim Brotherhood in Egypt.
The group was denied legal status once Zine el-Abidine Ben Ali took power in Tunisia in 1987. Nevertheless, the coalition won 17 per cent of the vote in the 1989 general elections.
Ghannouchi returned to Tunisia at the end of January after living nearly 20 years in exile, mostly in London. He still officially faces a life sentence for plotting against the president.
The new government has prepared an amnesty law for convicted activists like Ghannouchi, but it still needs to be voted on in the parliament.
Ghannouchi says he is more moderate than he was when the movement was founded. He said he would not run in the presidential elections to be held by mid-July, however the movement plans to run parliamentary candidates.
Meanwhile, on Tuesday three more ministers left the government, further weakening the interim ruling authority.
Ahmed Ibrahim, Minister of Higher Education and Scientific Research, who is the head of the Ettajdid party, said he could better serve his country working outside the government.
Minister of Local Development, Ahmed Nejib Chebbi, from the Progressive
Democratic Party, announced his resignation, and criticised the "hesitation and fuzziness" of the interim government.
Elyes Jouini, Minister for Economic and Social Reform resigned late Tuesday.
The three followed Sunday's resignation of Prime Minister Mohammed Ghannouchi, who stayed on as Prime Minister after Ben Ali was ousted.
Two other ministers who were also part of Ben Ali’s regime resigned on Monday: Technology Minister Mohamed Afif Chelbi and Planification and
International Cooperation Minister Mohamed Nouri Jouini.