But as two more British soldiers died in Iraq and a captive remained under threat of death, his hopes of bouncing back from wrecked public trust ratings are far from sure.
"The evidence about Saddam having actual biological and chemical weapons ... has turned out to be wrong," Blair said on Tuesday, his nearest yet to a mea culpa.
"The problem is, I can apologise for the information that turned out to be wrong but I can't, sincerely at least, apologise for removing Saddam," he said. "The world is a better place with Saddam in prison, not in power."
Blair's speech was interrupted twice by protesters, one yelling that the prime minister "had blood on his hands". They were quickly bundled out of the hall.
For most of his speech, Blair focused on domestic issues which he hopes will define his campaign to win a third term at a general election expected in May.
But aides said he knew that would not resonate with his party or the wider public, if he did not tackle Iraq head-on.
The prime minister made the case for war on the assertion that Saddam had weapons of mass destruction(WMDs) ready to use. The fact that none has been found more than a year after major military action ended has soured British public opinion.
Blair expressed support for captive
Kenneth Bigley and his family
"Whatever disagreements we have had, we should unite in our determination to stand by the Iraqi people until the job is done," he said.
Blair implied the invasion of Iraq was legitimate due to security fears in Britain - a line often taken by US President George Bush - and a change in his own initial stance.
"The only healing can come from understanding that the decision, whether agreed with or not, was taken because I believe, genuinely, that Britain's security depends on it.
"If I don't care and act on this terrorist threat, then the
day will come when all our good work on the issues that decide people's lives will be undone because the stability on which our economy ... depends, will vanish," he said.
He also mentioned British engineer Kenneth Bigley who is held captive in Iraq and the two soldiers killed in Basra on Tuesday.
"I want to express our condolences to the latest British
casualties in Iraq, and I want to, on behalf of all
of us, express our support and solidarity with Ken Bigley and
all the Bigley family."
Bigley's brother, Paul, has accused Blair of not doing enough to help secure the captive's release.