Marzouki, left, Jebali and Ben Jaafar are set to take up senior posts in Tunisia's new government [AFP]

Tunisia's three main parties have formalised a power-sharing agreement, 10 months after the ouster of Zine El Abidine Ben Ali, the north African country's deposed president.

Hamadi Jebali of the moderate Islamist Ennahdha party, which took the most votes in elections last month, will serve as prime minister, while the other senior posts of president and chairman of the new constituent assembly are divided between two left-wing parties.

Moncef Marzouki of the leftist Congress for the Republic Party (CPR by its French acronym) will be president, and Ettakatol's Mustapha Ben Jaafar will chair the body tasked with drafting a new constitution.

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The 217-member assembly will meet for the first time on Tuesday to confirm the three posts.

Jebali, 63, a moderate Islamist, is the deputy leader of Ennahdha, whose leader, Rachid Ghannouchi, is associated with a more hardline position on Islam.

Jebali's credibility comes in part from the fact that he spent 15 years in Ben Ali's jails. He speaks fluent French and has been at pains to allay fears that his party wants to impose an intolerant brand of Islam.

Marzouki, 66, also has a long track record of resistance to Ben Ali.

A doctor and the former president of the Tunisian human rights league, he was first jailed and then forced into exile until the deposed president's fall.

Ben Jaafar, 71, has been described by a colleague as a hand of steel inside a velvet glove.

While his gift for dialogue and affable manner helped keep him out of Ben Ali's jails, he never gave an inch on his principles, the colleague said.

The constituent assembly is dominated by Ennahdha, a party inspired by the Muslim Brotherhood, with 89 seats, while the CPR and the Ettakatol party control 29 and 20 seats respectively.

Sources said ministerial posts have also been assigned pending approval by the assembly.

Tunisia's revolt touched off a wave of pro-democracy protests across the region known as the Arab Spring.