Mr Hariri's bloc won the election but had to form a unity government
Lebanon's prime minister-designate Saad Hariri has formed a new 30-member unity government, ending five months of deadlock since the general election.
Fifteen ministers are from Mr Hariri's majority coalition, while five were nominated by President Michel Suleiman.
The remaining 10 ministers are from the opposition, including two members of the Islamist group Hezbollah, which struck a deal with Mr Hariri last week.
The deadlock over the new government had threatened Lebanon's stability.
"Finally, a government of national unity is born," Mr Hariri said, adding that it "opened a new page that we hope will be one of agreement and co-operation".
But the Western-backed leader also sounded a cautious note.
"This cabinet will either be a chance for Lebanon to renew trust in its institutions, or it will be a stage where the Lebanese will repeat their failure in achieving agreement," he said.
Mr Hariri, 39, spent more than four months agreeing the assignment of portfolios with the opposition groups in the unity government.
Correspondents say a meeting in October between the leaders of the two sides' main backers, Saudi Arabia's King Abdullah and Syrian President Bashar al-Assad, is thought to have helped heal the rift.
The Lebanese prime minister-designate's Sunni Muslim Future movement and its Maronite Christian and Druze allies have 15 ministers in the cabinet.
Hezbollah hold two of the new cabinet posts, one more than in the previous government. Its allies, the Shia Amal movement and the bloc of the Maronite Christian leader and former general Michel Aoun, have another eight.
Mr Aoun succeeded in retaining control of the telecommunications ministry, which his son-in-law Gibran Bassil previously ran. Mr Hariri had rejected a demand for Mr Bassil to be reappointed.
The post is considered sensitive because a government threat to shut down Hezbollah's private communications network in 2008 triggered bloody sectarian clashes throughout Lebanon between the Shia group and supporters of the pro-Western government.
The five remaining ministers, including those of interior and defence, were nominated by President Suleiman, who is considered a neutral.
They will hold the balance of power, as without them Mr Hariri's supporters will be unable to gain a simple majority, and the opposition will not be able to block decisions.
The opposition retained control of the key telecommunications ministry
One of Hezbollah's representatives in the cabinet, Mohammed Fneish, told the Associated Press that "this formula achieves the principle of real partnership in political decision-making on key decisions".
Meanwhile, UN Secretary General Ban Ki-moon welcomed the formation of the new government and called on it to "recommit to the full implementation of Security Council resolution 1701", which ended the 2006 war between Israel and Hezbollah.
"The secretary-general hopes that Lebanese political leaders will continue to work together in a spirit of unity, dialogue and co-operation," his spokeswoman said.
The government's first task will be to draw up a policy statement and present it to parliament for a vote of confidence. Mr Hariri is also expected to visit Damascus for the first time since his anti-Syrian coalition came to power in 2005.
The Syrian government was blamed for the assassination of his father Rafik, a former prime minister, in February that year, and eventually forced in its wake to withdraw its troops from Lebanon after 29 years. Damascus has denied any responsibility.