Speaking to Aljazeera on Sunday, al-Sadr said that if a new Iraqi government did not ask foreign forces to leave or set a timetable for their pullout, elections will have been useless.
"If elections open the door for the occupier to leave Iraq then it is a good thing. But if that is not the case, it will not have a real effect on the country or on Iraqis," he said.
"As long as the occupier is in Iraq, I will not take part in politics, whether in posts or the drafting of the constitution, because the occupier will intervene in one way or another."
But al-Sadr said all Iraqis should be allowed to participate in the country's political process, including Sunni Muslims, most of whom rejected the elections that handed power to Iraq's Shia.
"We must help the minorities to have an effective role in building the future of Iraq. Everyone must be given a chance to participate in building Iraq," he said.
Al-Sadr also urged Iraqis to refrain from violence against other Iraqis.
"I ask all parties to show patience and not to be dragged into the plots of the West which aim to destabilise the country and justify the presence of the occupation," Sadr said.
"Any attack on any Iraqi group is an attack on all Iraqis ... and it is wrong for a Muslim to kill a Muslim," he added.