The session -- held at a convention center in central Baghdad's heavily fortified Green Zone -- began with a formal prayer. One of the first speakers was Fouad Massoum, a Kurdish politician who headed the interim National Assembly under the interim government of Prime Minister Ayad Allawi. He said he was speaking on "a great day in Iraqi history."
UN special envoy to Iraq Ashraf Qazi congratulated the deputies, saying he was proud to witness history.
Iraqi interim President Ghazi al-Yawer also spoke and laid out the challenges ahead:
"The tasks of all Iraqis, in general, and, especially you [in the assembly], are big and important," al-Yawer said. "First of all is the writing of the constitution for Iraq, where all the rights of all segments of Iraqi society should be reserved, where all faiths and human dignity, freedom of expression should be respected. [The constitution] should ensure equality between all in a democratic, pluralist, federal Iraq with full sovereignty."
The National Assembly's main tasks are to choose the next interim government and to oversee the writing of the country's permanent constitution. If the constitution is accepted, Iraq will go to a new round of elections for a national government in December. If it is rejected, the National Assembly would be dissolved and a new one elected, extending the transitional period.
In his remarks on 16 March, Allawi said writing the constitution will be an arduous task, but that all sections of society should take part.
"The components of the constitution," Allawi said, "including the fundamental rights of citizens, the definition of the three authorities and the organization of the relationship between them, the shape of the state and the government and the laws made by man, are the parts which will make up a modern, civilized, and complete constitution which has an Iraqi specificity."
The session ended with the swearing in of the 275 deputies, elected in the 30 January vote.
The United Iraqi Alliance and an alliance of Kurdish parties won the two biggest blocs of seats in Iraq's elections on 30 January. But they have so far failed to reach agreement on a coalition government. The Shi'a alliance won 140 seats in the National Assembly but needs the Kurds' 75 seats for the two-thirds majority required to elect a president, who will then nominate a prime minister.
Allawi noted the sacrifices made by the Kurds: "Kurds made big sacrifices in this struggle [during the Saddam era]. This resulted and will result in the consolidation of national unity in our way forward."
The parties said on 15 March that they hoped to reach a comprehensive agreement this week.
Analysts say the 16 March gathering was significant but, in the absence of a government deal, largely ceremonial. They say the meeting does mark the beginning of a move toward a legitimately elected government in the country.
"You can have your elections and then what?" said Larbi Sadiki, a lecturer on Middle East politics at Exeter University in Britain. "So I think this is like the litmus test, you know, of how capable and how empowered the Iraqis are in reordering their own house without outside interference."
Sadiki says it may be the end of the month before a deal on the new government is reached.
The 16 March session took place as numerous explosions were heard outside. Smoke could be seen rising near the convention center, and air raid sirens sounded.
Speaking at the session, the leader of the United Iraqi Alliance, Abdel Aziz al-Hakim, said the new government must be tough on terrorists and anti-government militants. "[We need] a government that is able to uproot terrorism," al-Hakim said, "a government that can accelerate the trial of Saddam and the men of his regime and the remainder of his government."
The U.S. military says two mortar rounds landed inside the Green Zone but caused no injuries.
(RFE/RL's Iraqi Service contributed to this story.)