Iraq's Governing Council agreed on an interim constitution on Monday, marking a crucial step in Washington's plan to hand sovereignty back to Iraqis.
"There will be a signing ceremony on Wednesday," a council spokesman told the BBC.
The 25-member Council had previously missed a February 28 deadline to strike a deal amid divisions over the role of Islam, Kurdish autonomy demands and women in government.
"Islam will be the official religion of the state and it will be a source...of legislation," said the spokesman.
"Federalism also has been approved as a form of government," he said, adding details of the agreement would be announced on Wednesday.
The constitution is to provide a framework for an interim government set to take power on June 30 from the US-led administration in Baghdad.
The Council brings together leaders from Iraq's various ethnic and religious groups, including Shias, Sunnis, Kurds and Turkmen.
During discussions on Friday, several Shia members of the Council walked out, angered by the cancellation of a previous ruling that would have made divorce and inheritance subject to the rulings of religious law.
Other sticking points had included defining the role of women in a future government, with some Council members pushing for the constitution to set out a specific quota for the number of female representatives or parliamentarians.
There had also been furious debate over federalism, with the Kurds, who have effectively had self-rule in three northern provinces of Iraq since the 1991 Gulf War, pushing to enshrine that autonomy in the document.
Wednesday's signing ceremony will follow the celebration of an important Islamic festival Ashura, marking the martyrdom 1,300 years ago of Hussein (AS), a grandson of the Prophet Mohammad (PBUH).
Before Monday's announcement, an official in the US-led administration said US Governor Paul Bremer was unlikely to use his veto powers on a constitutional deal.
Officials said the negotiations were spirited and at times heated, but always respectful.