Anti-Islamist Beji Caid Essebsi, 88, was sworn in Wednesday as Tunisia's first freely elected president vowing to work for national reconciliation, four years after an uprising that sparked the Arab Spring.
The election of Essebsi, a veteran of previous regimes, is seen as a landmark for the North African nation, where longtime dictator Zine El Abidine Ben Ali was toppled in 2011.
Essebsi's victory over outgoing president Moncef Marzouki capped Tunisia's sometimes troubled transition to democracy and has won praise from Western leaders.
Essebsi told parliament after a swearing-in ceremony that he would be "the president of all Tunisians" and "the guarantor of national unity".
"There is no future for Tunisia without consensus among political parties and members of civil society," he said.
"There is no future for Tunisia without national reconciliation."
Essebsi also attended a handover ceremony at the presidential palace where he was embraced by the outgoing leader.
Marzouki, an exiled human rights activist during Ben Ali's rule, was elected president at the end of 2011 by an interim assembly under a coalition deal with the then-ruling moderate Islamist movement Ennahda.
Essebsi's Nidaa Tounes movement, which includes many members of Ben Ali's old ruling party, won landmark parliamentary elections in October.
Even so, the anti-Islamist lawyer has vowed a fresh start for Tunisia.
Essebsi took 55.68 percent of the presidential vote in a December 21 runoff against Marzouki -- the first time Tunisians have freely elected their head of state since independence from France in 1956.
In a presidential statement, Essebsi resigned as head of Nidaa Tounes on Wednesday in line with the constitution, and called for its deputy leader, Mohamed Ennaceur, to name a candidate to set up a new government.
Nidaa Tounes will need to form a coalition as with 86 MPs it fell short of an absolute majority in Tunisia's 217-seat parliament. Ennahda, which came second, has not ruled out joining a governing coalition.
Incumbent Prime Minister Mehdi Jomaa remains at his post until the formation of a new cabinet.
Opponents have accused Essebsi of seeking a return to the era of Ben Ali, who clung to power for 23 years, combining authoritarian rule with a degree of prosperity and stability for his people.
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During campaigning Essebsi accused Marzouki of representing the Islamists, whom he says have "ruined" the country since the revolution, and many voters appeared to be seeking a return to stability.
Following independence, Essebsi became an adviser to the country's founding father and first president, Habib Bourguiba, holding a number of key jobs under him and then Ben Ali.
He later returned to the public stage as a supporter of the 2011 uprising and served as prime minister briefly after Ben Ali's ouster while elections were organised for the interim assembly.
- Big challenges ahead -
The revolution that began in Tunisia spread to many parts of the Arab world, with mass protests in Egypt, Libya, Syria and Yemen.
In every country except Tunisia the revolution was followed by violent turmoil or, as in Syria's case, a devastating civil war.
Essebsi and the new government will face major challenges.
Tunisia's economy is struggling to recover from the upheaval of the revolution and there is a growing threat from militants long suppressed under Ben Ali.
Essebsi said it was his duty to address economic problems "to realise the promises of the revolution: dignity, employment, health and regional equality."
Tunisian newspapers urged the new leadership to uphold the dreams of the revolution.
"All the vicissitudes of history during the past 40 years show the importance of respect for human rights," Le Temps said.
It said there was "no question of backtracking on respect for freedoms".
La Presse said Tunisia's experience showed that "democracy is compatible with Arab-Muslim culture".
It added: "Now we must demonstrate that this democracy can be turned into economic opportunity and prosperity."