The agreement, reached in an effort to draw Sunni support for the document, calls for a review of the constitution once Iraqis elect a new legislature in December.
"Today is an historic day," Iraqi President Jalal Talabani, who announced the deal, said according to Radio Free Europe. "I am confident that there will be a consensus on the constitution on the day of the vote."
Sunni leaders had urged Iraq's Sunni Arab population to vote "no" to the draft constitution, but on Wednesday, the country's main Sunni political party, the Iraqi Islamic Party, said it would now encourage a "yes" vote.
Iraq's three main ethnic groups have been at odds over the constitution's call for a federal, democratic state. Sunni leaders believed autonomous Shiite and Kurdish regions of the country could lead to the Sunni minority's marginalization.
The last-ditch deal creates the possibility of later amendments to the constitution, restricting Kurdish self rule, Iraqi Islamic Party leader Baha Aldin al-Naqshabandi said in an interview with RFE.
"Regarding federalism, the Iraqi Islamic Party only admits the federalism of Kurdistan," he said. "But for the other regions of Iraq, the Iraqi Islamic Party cannot accept this federalism because it will divide Iraq into many countries."
Sunni groups also have taken issue with the use of the Arabic language by non-Arab Kurds in Kurdistan. There was some confusion about whether the deal included a clause addressing that concern.
While Naqshabandi and his party endorsed the newly revised draft, other Sunni leaders condemned the deal, which U.S. envoy in Iraq Zalmay Khalilzad helped broker.
"This is a ploy to persuade people not to vote 'no' to the ethnic and sectarian racist constitution," the Iraqi National Dialogue said in a statement on behalf of 19 Sunni groups, according to Reuters.
"We ask people to go and vote 'no' to this constitution," the group's spokesman Saleh al-Mutlak said.
As Iraq's political leaders worked to create a more unified country, insurgents angry by the U.S. involvement in drafting the constitution wreaked havoc in several areas of the country, hoping to dissuade voters from going to the polls.
In the Syrian border town of Tal Afar, about 250 miles north of Baghdad, a suicide bomber killed at least 30 police recruits at a military base. The bomb injured another 35 people. The blast was the second suicide bombing in two days. On Tuesday, also in Tal Afar, a suicide car bomber killed 30 people and wounded 45 in a crowded outdoor market.
The terrorist network al-Qaida claimed responsibility for both attacks, Reuters reported.
Meanwhile Wednesday, a suicide car bomber wounded seven Iraqi soldiers and two civilians at a checkpoint in Baquba, northeast of Baghdad. Another suicide car bomber targeted Iraq's minister of state for the provinces, Saad Nife al-Herdan, Reuters reported. The politician escaped but four of his bodyguards and three civilians were wounded.
As U.S and Iraqi forces continued to battle a Sunni-led insurgency against the Kurdish and Shiite-led government in Baghdad, two U.S. soldiers died Wednesday when their vehicle rolled over during a patrol.