The British Prime Minister's pledge - which will be seen by critics as a 'blank cheque' for military support for the US-led action - came eight months before the conflict started in March 2003.
Blair's words emerged in full for the first time in one of 30 different notes, handwritten letters, emails and memos sent to the US President before, during and after the invasion.
The missives reveal that soon after the 9/11 terror attack on the twin towers in New York, Blair and Bush were in close, often personal, contact over how to topple Saddam Hussein and remove the threat of his alleged Weapons of Mass Destruction (WMD).
Bush's replies have not been published, but Blair's notes are reproduced for the first time. Normally under a 30-year rule imposed by Whitehall, such messages between Prime Ministers and Presidents are not published for decades.
But Sir John Chilcot won a battle with the Government, security agencies and Downing Street to allow them to be printed.
Here are the key extracts.
1. 'This will require action that some will baulk at'
12 September 2001
The day after 9/11, Blair sent Bush the first of many notes. And WMD was first in his thoughts - as well as military action.
"There will be many who ask: what is the next stage of this evil? What of their capacity to get hold of biological, chemical and other WMD? We know that there are countries and individuals trading in WMD and/or trying to acquire them. We need a range of sanctions and pressure to stop this.
"Some of this will require action that some will baulk at. But we are better to act now and explain and justify our actions than let the day be put off until some further, perhaps even worse catastrophe occurs."
"It would also help in the Islamic world if we could find a way to revive the Middle East Peace Process"
2. 'A tightly knit propaganda unit' is required
11 October 2001
In a section titled 'Extending War Aims', Blair wrote there was "a real willingness in the Middle East to get Saddam out but total opposition to mixing this with the current operation" in Afghanistan.
The idea of a "Phase 2" in the war on terror was "really hurting..because it seems to confirm the UBL [Osama bin Laden] propaganda that this is West v Arab".
Blair added that he had "no doubt we need to deal with Saddam"
"But if we hit Iraq now, we would lose the entire Arab world, Russia, probably half the EU...I am sure we can devise a strategy for Saddam deliverable at a later date"
He added that of Phase 2, "we just don't need it debated too freely in public until we know what exactly we want to do and how we can do it"
Blair concluded that "a dedicated tightly knit propaganda unit" was required.
7 November 2001
Blair met Bush in Washington and passed him a note during their private meeting. The note had a section 'International Initiatives' which referred to the need for a new UN resolution on Iraq and a wider 'WMD agreement'.
3. The need to be 'softening up' public opinion.
4 December 2001
Blair wrote a paper for Bush titled 'The War Against Terrorism: The Second Phase'. It said Iraq 'has WMD capability, is acquiring more'. It said any link between Iraq and 9/11 and Al Qaeda was 'at best very tenuous'. He called for a 'strategy for regime change that builds over time', but made clear the West should only get involved by helping rebel groups and uprisings from within Iraq.
Blair talked about 'softening up' public opinion by working with UN inspectors.
4. 'I will be with you, whatever'
28 July 2002
Blair sent a note to Bush to persuade him to use the UN to build a coalition for action against Iraq.
"I will be with you, whatever. But this is the moment to assess bluntly the difficulties. The planning on this and the strategy are the toughest yet. This is not Kosovo. This is not Afghanistan. It is not even the Gulf War."
Blair also showed how keen he was for military action in coming months.
"We would support in any way we can....On timing, we could start building up after the break. A strike date could be Jan/Feb next year. But the crucial issue is not when but how.”
Blair said that "right now" he "couldn't be sure of support from Parliament, party, public or even some in the Cabinet".
He added that it would be best to go down the UN route because Saddam would "probably screw it up and not meet the deadline" of weapons inspections.
Blair sketched out a strategy to help swing round British public opinion:
"If we recapitulate all the WMD evidence; add his attempts to secure nuclear capability; and as seems possible, add on the Al Qaida link, it will be hugely persuasive over here. Plus..the abhorrent nature of the regime".
5. 'It was a brilliant speech...Well done'
12 September 2002
Blair wrote a handwritten note to Bush praising his UN General Assembly speech, which had set out the case for war if Saddam refused to comply with the UN.
"It was a brilliant speech. It puts us on exactly the right strategy to get the job done....Well done"
6. 'We will carry people - even without the 'smoking gun'"
24 January 2003
The day after MI6 chief Sir Richard Dearlove advised Blair that the US had 'in effect' already taken the decision to use force against Iraq, Blair wrote to Bush arguing the need for a second UN resolution.
"Technically we are right. 27 January should be crunch time. But we won't carry other people...If [UN inspector] Blix carries on reporting non-cooperation...and hardens his findings with each stage, I think we will carry people - even without the 'smoking gun' [of WMD] - shortly".
There were "big majorities against action without UN backing everywhere, even in the UK" and "even in the Cabinet". The US and UK had invested a lot in the UN route so to abandon it would lose a "big comfort blanket". If a second resolution attempt was abandoned, it would be "about US power, naked and in your face".
7. 'They fear we are hell bent on war'
19 February 2003
Blair wrote a lengthy note to Bush suggesting a second UN resolution could be pitched as an 'ultimatum' to Saddam. He also suggested that a Middle East "road map" would "have a massive impact in Europe and the Arab world".
He added there was "a need to start firming up the humanitarian work for the aftermath of the conflict...and show how we will protect and improve the lives of the Iraqi people".
Blair says the public:
“are not against conflict in all circumstances. What they fear is that we are hell bent on war, come what may - that we don't really want the UN to succeed.”
8. Blair's 'New World Order'
March 26 2003
In a note to Bush titled 'The Fundamental Goal', Blair set out his wider thoughts on why the Iraq War would prove historic: a new 'world order'.
“This is the moment when you can define international priorities for the next generation – the true post-Cold War world order. Our ambition is big – to construct a global agenda around which we can unite the world”.
Blair said the war would be part of a bigger push to “spread our values of freedom, democracy, tolerance and the rule of war” across the world.
“That's why, though Iraq's WMD is the immediate justification for action, ridding Iraq of Saddam is the real prize.”
9. Those marching against war were 'defending' Saddam
March 26 2003
Blair also complained about those marching against the war, claiming they were 'defending' Saddam, and suggested European leaders were motivated by a hatred of the US 'Right'.
"The ludicrous and distorted view of the US is clouding the enormous attraction of the fundamental goal. In the past weeks I have had conversations with intelligent Europeans which has vividly illustrated this for me."
One European leader “seriously compared" Donald Rumsfeld with Osama Bin Laden. Some Europeans wanted to “substitute the relationship with the US for one with Russia”.
“In other words, rational people are behaving very stupidly."
The public were getting “wholly warped views of the so-called right in American politics”
"We end up with the fatuous irony of millions of liberal-minded people taking to the streets, effectively to defend the most illiberal regime on earth”.
10. 'If it falls apart, everything falls apart'
2 June 2003
After the invasion, Blair wrote a note to Bush in which he admitted the dangers of not properly planning a proper post-war reconstruction.
"The task is absolutely awesome and I'm not at all sure we're geared for it. This is worse than rebuilding a country from scratch. My sense is: we're going to get there but not quickly enough. And if it falls apart, everything falls apart in the region."
11. 'It better be going right'
5 June 2003
Blair warned Bush in a new note of the dangers of sorting the post-war situation. And he had his first hints of a political joint problem.
"It may be odd for a Labour Prime Minister and a Republican President to have a common political interest, but we do!"
"By this time next year, it better be going right, not wrong, for us and for the world!"
12. Iraq will be 'a major problem' for Blair's election
5 October 2003
Blair told Bush of his worries about the impact on his chances of winning the 2005 general election:
"My political position is very clear. I won't win re-election on Iraq alone. But if Iraq is wrong or people don't get the security threat, it will be a major problem"
13. First worries about no WMD
1 February 2004
Blair wrote a 'note on WMD' as it began to appear that none could be found in Iraq.
"If we have to accept that some of the Iraq intelligence was wrong, we will do so. But let us not either a) lurch to the opposite extreme and start pretending Iraq had nothing; or b) let any intelligence inaccuracy move us off confronting the WMD issue."
14. Still optimistic about post-war Iraq
22 May 2006
Blair sent Bush a note after a visit to Baghdad stating:
"I left Iraq, on balance, more optimistic not less...The Government obviously has a clear sense of mission..."
But he warned that "the nature of the insurgency is changing...hence Basra becoming a problem".
15. More political problems looming
9 November 2006
Blair warned Bush of their joint political problems if Iraq went wrong. He said that the US Democrats - usually allies of the British Labour Party - could take advantage against Bush's Republicans.
"Our foreign policy is so joined, we both face the same issues. So a Democrat victory is seen here as a 'thumping' for me as well as you!".
16. The Iraqis need to start taking over
After a trip to Iraq, Blair wrote to Bush about the prospect of a US troop surge to help security.
UK troops had "surprisingly high morale". On a troop surge "it might be sensible short term but only as part of a wider plan to boost Iraqi capability...That has to be Iraqi force, plus reconstruction".