Prime Minister Habib Essid and his team took the oath of office in front of President Beji Caid Essebsi before an official handover from interim premier Mehdi Jomaa.
Essid vowed to fight for greater democracy and greater regional stability, four years after a revolution ousted longtime dictator Zine El Abidine Ben Ali, and against rampant unemployment.
"The traditional solutions and sedatives are no longer enough," he said in a speech.
Both Essid and Essebsi, who was elected in December, paid tribute to Chokri Belaid, an anti-Islamist politician shot dead by suspected jihadists exactly two years ago, with the premier vowing to track down the assassins.
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Nidaa Tounes, which won legislative elections in October, holds six portfolios including the foreign ministry, while the interior, defence and justice portfolios have gone to independents.
Ennahda has the labour ministry and three secretary of state posts.
Nidaa Tounes won 86 of parliament's 217 seats in October, while Ennahda came in second with 69.
Essid announced his cabinet Monday after dropping his initial team when Ennahda warned it would vote against any line-up that excluded it.
He has said the government's "top priority... Will be one of providing security and the battle against terrorism".
Tunisia's security forces are battling jihadists who have claimed responsibility for a series of attacks on police and soldiers that have killed dozens of people since Ben Ali's ouster.
Additionally, some 2,000-3,000 Tunisians, many holding dual nationality, are believed to have joined jihadists fighting in Iraq and Syria.