The new deal revived hopes of winning Sunni Arab support for the charter in this weekend's referendum. But the National Assembly could have trouble getting a quorum on Wednesday.
A month-long legislative recess began on Monday, and many legislators had returned to their provinces for Saturday's referendum vote, and to spend the month of Ramadan with their families.
To improve security for the referendum, a four-day national curfew also begins on Thursday, and a holiday has been called for the ballot.
Still, Parliament speaker spokesman Muhanad Abd al-Jabar said the assembly must meet at 7pm on Wednesday to vote on the final version of the draft constitution incorporating Tuesday's last-minute compromises.
He said lawmakers who rushed back to Baghdad for the special session would be flown home afterwards at the government's expense.
If a quorum is reached, the vote could simply be a formality since most of the lawmakers generally follow their party leaders.
Lawmakers will be flown back to
attend the session
The last-minute deal was clinched on Tuesday after days of intense negotiations.
Shia and Kurdish leaders agreed to concessions that would see parliament consider amendments to the charter after new legislative elections are held in December.
The main Sunni Arab party said it would now be calling for a "yes" vote on Saturday, when 15.5 million registered voters are to cast their ballots on the document that lays out the legal framework for the new Iraq.
"There was an agreement and we are calling for a 'yes' vote," Ayad al-Sammarai, spokesman for the Iraqi Islamic Party, told AFP. "It will give us the opportunity to review the constitution."
Another Iraqi Islamic Party official, Ammar Wajih Zain al-Abidin, who is a member of the party's political bureau, told Aljazeera from Baghad: "We have been assured of the addition of an article to the constitution, stating that the parliament forms a special committee, representing all major sectors of the Iraqi society, to revise the constitution.
"This committee will present an assessment of the constitution within four months," he said.
"The report should include the required amendment," Zain al-Abidin said.
"The amendment would be proposed with the referendum if it is approved by a parliamentary majority," he added.
Zain al-Abidin believes that the referendum will be successful if the constitution is approved by a majority of voters in Iraq.
"Our previous stand was to reject the constitution due to the clear legal violations in it..."
Ammar Wajih Zain al-Abidin,
Iraqi Islamic Party official
"Our previous stand was to reject the constitution due to the clear legal violations in it and lack of flexibility of other parliamentary blocs," he said.
"However, this additional article has actually given us the chance to be able to amend some articles in the constitution after four months, which will serve the interests of all sectors of the Iraqi society," he added.
Most Sunni Arabs are opposed to the federal provisions of the draft, fearing it could lead to the break-up of the country.
The constitution will be adopted if a majority of voters approve the text and if two-thirds of voters in three or more provinces do not reject it.
Jawad al-Maliki, the number two in Prime Minister Ibrahim al-Jaafari's mainly Shia party Dawa, said a committee to be set up after the December vote would have four months to consider possible amendments to the charter, which will then be put to another referendum.