"We cannot and will not leave Iraq until victory is achieved," he said.
The president said that Thursday's parliamentary elections in Iraq would be a watershed moment that would inspire democracy across the Middle East.
But with public opinion still running against his mission, Bush still was left defending his decision to go to war nearly three years ago.
"It is true that much of the intelligence turned out to be wrong. As president I am responsible for the decision to go into Iraq," Bush told a foreign policy forum on the eve of elections to establish Iraq's first permanent, democratically elected government.
"And I'm also responsible for fixing what went wrong by reforming our intelligence capabilities. And we're doing just that.
"We are in Iraq today because our goal has always been more than the removal of brutal dictator," Bush said.
"It is to leave a free and democratic Iraq in his place.
Americans less optimistic
"My decision to remove Saddam Hussein was the right decision. Saddam was a threat and the American people and the world is better off because he is no longer in power," the president told the Woodrow Wilson International Centre for Scholars.
Bush insists his decision to
remove Saddam was the right one
Most Americans see progress on establishing democracy in Iraq, but they are less optimistic about efforts to prevent a civil war and reduce the number of civilian casualties, polling found.
Fifty-six percent said they thought progress was being made in the establishment of democracy, but almost as many - 53% - said they thought the United States was losing ground in reducing civilian casualties, according to the poll by the Pew Research Centre for the People & the Press.
Banking on election
As he usually does, Bush asserted that the Iraq of the future, with a functioning democracy and thriving economy, would be a model for other nations in the turbulent Middle East.
But he added a specific reference to the inspiration that a free Iraq could provide to reformers in the region's two governments most hostile to the United States - Syria and Iran.
Iraqis will vote in parliamentary
elections on Thursday
The president is banking on a successful election to signal that his war plan is working.
If the voting establishes a successful government, it eventually could lead to the withdrawal of US forces.
Bush could use more good news in Iraq.
More convincing needed
With the violence showing no sign of waning, most Americans are unhappy with his handling of the war, and some lawmakers are questioning how long the troops should stay.
At a news conference before Bush's speech on Wednesday, Harry Reid, the Senate minority leader, said: "Tomorrow's elections must signal a turning point in the relationship between America and Iraq."
The Nevada Democrat said that judging by the last three Iraq speeches, the president "is still not focused on what needs to be done in convincing the American people and showing the American people what his plan is in Iraq".