Writing in The Observer, Tutu said he had "no choice but to spurn Blair" by pulling out of a speaking engagement at a conference in Johannesburg last week where the former prime minister was also due to speak.
The Archbishop condemned the "immorality" of the decision by the US and Great Britain to invade Iraq in 2003, saying it had "destabilised and polarised the world to a greater extent than any other conflict in history".
He said: "On what grounds do we decide that Robert Mugabe should go the International Criminal Court, Tony Blair should join the international speakers' circuit, bin Laden should be assassinated, but Iraq should be invaded, not because it possesses weapons of mass destruction, as Mr Bush's chief supporter, Mr Blair, confessed last week, but in order to get rid of Saddam Hussein?"
The Archbishop pointed to the "staggering" human cost of the invasion, namely the deaths of an estimated 110,000 Iraqis and nearly 4,500 US soldiers.
"On these grounds alone, in a consistent world, those responsible for this suffering and loss of life should be treading the same path as some of their African and Asian peers who have been made to answer for their actions in the Hague," he said.
Tutu warned that the cost beyond the death toll was the "hardened hearts and minds" of people around the world.
"Has the potential for terrorist attacks decreased? To what extent have we succeeded in bringing the so-called Muslim and Judeo-Christian worlds closer together, in sowing the seeds of understanding and hope?" he said.
"Leadership and morality are indivisible. Good leaders are the custodians of morality. The question is not whether Saddam Hussein was good or bad or how many of his people he massacred.
"The point is that Mr Bush and Mr Blair should not have allowed themselves to stoop to his immoral level."