The committee preparing next month's Iraqi national conference says it has invited the radical Shia cleric, Moqtada Sadr, to take part.
It is not clear whether Mr Sadr has accepted
The head of the committee, Fuad Maasum, said Mr Sadr had begun to transform his militia into a political organisation.
Supporters of Mr Sadr launched a revolt against US-led forces in April, after the Americans ordered his arrest on charges of murdering a rival cleric.
However, a truce was agreed earlier this month.
Since then, US officials have referred to his possible trial as an internal Iraqi matter.
Mr Sadr also gave his provisional support to Iraq's interim government, which he had previously described as an American puppet.
Some 1,000 people from across Iraq are being invited to next month's conference, which will select a national council to advise Iraq's interim government.
The council will serve until elections are held, and will have the power to approve the budget for 2005.
It will also be able to veto legislation with a two-thirds majority, call ministers in for questioning over policy and pick a new president or deputy president if one dies in office.
It is not yet clear whether Mr Sadr will accept the invitation.