Adnan Pachachi said the session had been delayed to allow political groups more time to agree on key government posts.
The move comes a day after Shia politicians suggested a formula to replace their nominee for prime minister to break the deadlock over a new unity government.
Two Shia officials, speaking on condition of anonymity because of the sensitivity of the discussions, said on Satuday the formula called for Ibrahim al-Jaafari, the prime minister, to step aside in favour of another candidate from his Dawa party.
In return, the biggest Shia party, the Supreme Council for the Islamic Revolution in Iraq, would not push one of Iraq's vice-presidents, Adil Abdul-Mahdi, for the post, the officials said.
It was unclear whether al-Jaafari had signed off on the plan, and it appeared there was no agreement even among Dawa on a replacement.
Al-Jaafari defeated Abdul-Mahdi for the nomination in a vote among Shia lawmakers in February and has refused to step down.
Pressure for resolution
Sunni and Kurdish opposition to al-Jaafari has stalled efforts to form a unity government four months after parliamentary elections.
Shia officials are under pressure from the Americans, the British and the Shia clerical hierarchy to resolve the premiership issue so a government can take power.
Iraqis in Basra demonstrate in
support of al-Jaafari (file)
On Friday, representatives of the main political blocs agreed to create a six-member committee to choose names of candidates for the posts of president, vice president and prime minister, said Mahmoud Othman, a Kurdish elder statesman.
There had been plans for the committee to present this candidate list to heads of each political bloc in the hope of having an agreed list before parliament sat.
Meanwhile, violence has continued across Iraq, with at least 17 dead in two car bombings and a bus shooting.
In the worst incident, at least eight people were killed after a car bomb exploded near a market in Mahmudiya, south of Baghdad, police sources said.
US forces also killed five suspected militants in a raid southwest of the capital, Baghdad.
One woman died and three women and a child were injured in the raid in Yusifiyah.
A British soldier also died on Saturday from injuries sustained in a roadside bomb attack in the southern city of Basra, the UK ministry of defence said.