Labor leader Kevin Rudd made the remarks a day after ordering his country's 550 combat troops to head home after five years in Iraq.
As one of the United States' staunchest allies, Australia was quick to pledge military support for the US-led coalition invasion of Iraq in 2003. But that decision was made by conservative prime minister John Howard, whose 11 years in office came to an end in November's election.
Bringing home Australia's small but politically significant contingent of combat troops was one of Mr. Rudd's main election campaign pledges.
He dismissed one by one the reasons used by the Howard administration – and by association the Bush administration – to topple Saddam Hussein.
"Have further terrorist attacks been prevented? No, they have not been, as the victims of the Madrid train bombing will attest," Rudd told Parliament.
"Has any evidence of a link between weapons of mass destruction and the former Iraqi regime and terrorists been found? No.
"Have the actions of rogue states like Iran been moderated? No ... Iran's nuclear ambitions remain a fundamental challenge.
"After five years, has the humanitarian crisis in Iraq been removed? No, it has not."
Rudd said there had been a "failure to disclose to the Australian people the qualified nature of the intelligence. For example, the prewar warning that an attack on Iraq would increase the terrorist threat, not decrease it."
In response to Rudd's remarks, White House spokeswoman Dana Perino told reporters Monday that "we acted on the intelligence that we had.... No one else in the world, no other government, had different information and so we acted based on what was the threat that was presented to us."
Rudd, a former diplomat, also dismissed his predecessor's argument that Australia had been obliged to send troops to Iraq because of its longstanding alliance with the US. He said that while he valued the alliance, it did not mean that Canberra should automatically accede to US requests for military support.
Australia's defense minister, Joel Fitzgibbon, said that the country's military was overstretched with commitments in East Timor, Afghanistan, and Iraq. "Roughly half of our infantry and cavalry is somehow tied to those deployments. This is an unsustainable position," he said.
But Rudd said Australia would continue to keep its 1,000 troops now deployed in Afghanistan.
Brendan Nelson, leader of the opposition Liberal Party, said Australia's troops should stay in Iraq and continue their a training role. .
Australian troops helped train 33,000 Iraqi Army soldiers and did reconstruction and aid work.
Rudd said 27 Australian soldiers had been wounded in Iraq since 2003. None had been killed.
Australia will still have about 800 military personnel in and around Iraq, including a 110-strong diplomatic security detachment in Baghdad, sailors on warships in the Persian Gulf, and Royal Australian Air Force crew.
• Material from the Associated Press was used in this report.