Tunisian dissident Mohsen Marzouk opened a congress of his new party on Saturday, rejecting religion in politics and vowing to be a force for change.
Marzouk launched the Tounes Movement Project in March, basing his policies on those of independence leader Habib Bourguiba.
More than 3,000 people attended Saturday's opening of the constitutional congress in Tunis, which will continue for the next two days in the northeastern town of Hammamet.
"We are in total disagreement with all those who mix politics and religion," Marzouk said, referring to the Islamist Ennahda party, which controls the most seats in parliament.
"The time has come to reform the country. We are the party of reform and we have decided to be a force for constructive plans," party founding member Mondher Belhaj Ali told AFP.
Marzouk stepped down down as secretary general of Nidaa Tounes after a split with the president's son, Hafedh Caid Essebsi, over who should take over as leader.
Tensions came to a head in October after accusations that Essebsi supporters wielding sticks had blocked rival party members from a meeting of its executive committee.
The crisis saw 22 lawmakers leave Nidaa Tounes in January to form their own Al-Horra (The Free) bloc, making Ennahda the largest group in parliament.
Nidaa Tounes now has only 64 MPs as against 69 for Ennahda.
Nidaa Tounes was created in 2012 and included political personalities from the left and centre right, as well as officials from the former regime of toppled ruler Zine El Abidine Ben Ali.
The political backbiting comes as Tunisia, the cradle of the Arab Spring, has been gripped by protests against poverty and unemployment in the worst social unrest since the 2011 revolution.