Sir John Chilcot outlined his findings on the UK's involvement in the 2003 Iraq War in a critical report, containing more than 2.3 million words, spanning nearly a decade of United Kingdom government policy decisions between 2001 and 2009.
The inquiry, which was given unprecedented access to confidential government documents and took longer to complete than British military involvement in the conflict itself, said Blair had relied on flawed intelligence and determined the way the war was legally authorised was unsatisfactory.
An emotional but defiant Blair told a news conference that going to war in Iraq was "the hardest, most momentous, most agonizing decision I took" as prime minister.
However, Sir Chilcot says the chaos in Iraq which followed the invasion should have been foreseen.
The official inquiry into the 2003 war was strongly critical of Mr Blair's government and United Kingdom military chiefs.
"He will be remembered not as a prime minister but as a person who sent them on an illegal war".
"The invasion and subsequent instability in Iraq had, by July 2009, also resulted in the deaths of at least 500,000 Iraqis - and probably many more - majority civilians". "Military action at that time was not a last resort", he said. Lord Goldsmith commented yesterday: 'In purely technical terms, legal opinions can differ.
"The people of Iraq have suffered greatly", he said. In my opinion, that decision was in accordance with global law and it was permissible for those with the responsibility for taking the decision to proceed.
Humphrys suggested some people thought Mr Blair was deluded.
"There is no question that that ill-fated intervention by Blair and Bush precipitated some of the chaos we see in the region today".
In his 12-volume document, Sir John placed the burden of responsibility on Blair and revealed the extent of his alliance with the then U.S. president George W. Bush to whom he promised an unconditional support for the invasion of Iraq in 2002.
Following the publication of the report, Mr Blair said he took responsibility for "mistakes in planning and process" identified by the inquiry.
Mr Howard said one of the most relevant findings to come out of the report was that there was no evidence to support claims that intelligence used to justify the war on Iraq had been doctored by Western governments.
The fact is that the invasion of Iraq and the start of a war that continues to this day, not only did it turbo charge al-Qaida back then, but it created the circumstances for the rise of Islamic State.
The 2003 invasion of Iraq was the most unpopular war in British history. However he insisted the world is a better place because of the removal of Saddam.
Many will now want Blair, who they call a war criminal with blood on his hands, to face some sort of prosecution - and the Chilcot report has left that door open. "There were errors in intelligence, but there was no lie", he said.
It eviscerated Blair's style of government and decision-making.