The two million-word report, six years in the making, will be unveiled by John Chilcot tomorrow.
Tony Blair, prime minister when Britain went to war, has said he will not make any comment until the report is made public.
The International Criminal Court (ICC) has indicated the former Labour leader will not be liable for prosecution, reiterating its conclusion 10 years ago that the decision to go to war is not within its jurisdiction.
The court said it will look at the report’s findings before deciding whether there is a “reasonable basis” to begin an investigation.
In a statement, the Office of the Prosecutor at the ICC said: “We will take note of the Chilcot report when released in the context of its ongoing preliminary examination work concerning Iraq/UK.
"A preliminary examination is not an investigation, but a process aimed at determining whether reasonable basis exist to open an investigation.
“As already indicated by the office in 2006, the ‘decision by the UK to go to war in Iraq falls outside the court’s jurisdiction’.”
Blair said: “I have taken the view, I think rightly or wrongly, we should wait for the report to be published and then I will express myself and I’m not getting into either the politics or the detail of it until I’ve actually seen it.”
A number of MPs are expected to try to use an ancient law to try to impeach the former prime minister once the findings are published.
Former Scottish first minister Alex Salmond said there “has to be a judicial or political reckoning” for Blair’s role in the Iraq conflict; shadow chancellor John McDonnell said the “processes” of how Britain ended up at war must be examined “so we never ever get into this tragic, tragic mess again with such loss of life”.
Some of those whose loved ones died in the war between 2003 and 2009 fear the report will not give them the answers they desperately want.
Gary Nicholson, 42, was one of 10 servicemen who died when their Hercules C-130 aircraft was shot down in 2005.
His mother Julia said: “It will be a whitewash. I’m absolutely disgusted. I’m not going because it will be a whitewash.
“Tony Blair has got blood on his hands. He will have covered his back and (George) Bush’s back.”
Janice Procter, whose son Michael Trench, 18, was one of the youngest British soldiers to die in Iraq when he was killed in 2007, said: “It’s been horrendous, I’m very apprehensive about this.”