• The PM will have the opportunity to distance himself from Blair's decision to go to war
Senior sources at Number 10 are expecting an announcement to be made today at 10am.
A spokesman for the head of the inquiry, Sir John Chilcot, confirmed that he had written to the Prime Minister last night saying the panel would be "happy to offer him the opportunity" to appear before the election.
Sir John had previously ruled the Prime Minister's evidence should be delayed to keep party politics out of proceedings.
But, after mounting political pressure for Mr Brown to appear before the panel in advance of the election which must be held by 3 June, he has now amended his original decision.
Mr Brown has publicly insisted he has "nothing to hide" and has told Sir John he was willing to appear "at any time" the inquiry should wish.
A move by Sir John to call Mr Brown could offer the Prime Minister the opportunity to distance himself and his party from any fallout surrounding Tony Blair's decision to go to war on the basis of the infamous weapons of mass destruction (WMD) intelligence report.
Demands for Mr Brown's evidence to be brought forward were heightened this week after he was accused of starving the armed forces of essential funds.
And in his evidence last week, Tony Blair's former spin chief, Alastair Campbell, said Mr Brown was part of the "inner circle" of ministers and advisers the then premier consulted in private on Iraq.
Mr Blair is due to give his evidence to the inquiry a week today.
Responding to a rising tide of calls for him to give evidence before the election, Mr Brown yesterday told MPs he had written to the Iraq inquiry committee stressing his willingness to do so but saying he would listen to Sir John's advice on the matter.
"I have written to Sir John Chilcot, and I have said to him that I am happy to give evidence at any time," the Prime Minister said. "That is a matter for the committee to decide, but I will take whatever advice he gives me about when he wishes me to appear.
"I am happy to give evidence about all the issues that he puts forward, and I am happy to satisfy the public of this country about our government's commitment to the security of this country."
Last week, Mr Brown insisted he had "nothing to hide", when Liberal Democrat leader Nick Clegg said the public were entitled to know his role in the government's "most disastrous decision" before casting their votes.
Angus Robertson, the SNP leader at Westminster, who raised the issue at Prime Minister's Questions on Wednesday, said: "The net is closing in on Gordon Brown. Despite all his efforts to force the Iraq inquiry behind closed doors, the case for the man who bankrolled the illegal war in Iraq to give full evidence in public is overwhelming – and now even he has acknowledged that.
"Tony Blair led us into the worst foreign policy disaster in modern times and, as senior figures involved in the run-up to the conflict have already told the Chilcot inquiry, Gordon Brown was right beside him all the way.
"The people deserve the whole truth about a war fought in their name, but the full facts cannot be known until Gordon Brown is held to account for his actions."
Former Liberal Democrat leader Sir Menzies Campbell said Mr Brown had "bowed to the inevitable".
He added: "It would have been incomprehensible to the general public if he had not been called to give evidence before the election, along with other members of the Cabinet at the time of the decision to take military action against Iraq, like Geoff Hoon and Jack Straw."
Mr Straw, who was foreign secretary at the time of the United States-led invasion and is now Justice Secretary, gave evidence to the inquiry yesterday. He admitted he only "very reluctantly" came round to supporting the military action and said he presented Mr Blair with an alternative plan on the eve of the crucial Commons vote on war which did not involve committing British troops alongside the Americans.
He said his support for the invasion had been "critical" if UK forces were to be involved, as Mr Blair could not have carried the government and parliament without him. But while he had not actually considered resigning, he nevertheless said he had weighed his responsibilities in relation to the policy on Iraq "very heavily".
Throughout his evidence, he repeatedly appeared to suggest that his views were at odds with Mr Blair, saying, while he owed the then prime minister his loyalty, they were "two different people".
A policy that simply sought to overthrow Saddam Hussein – as the Americans were advocating – would have been "improper and self-evidently unlawful" and he would not have gone along with it.
Throughout the build-up to the invasion, he said he had always believed it was possible to resolve the crisis over Saddam's supposed WMD without the need for military action.
And he bitterly attacked both former French president Jacques Chirac and chief United Nations weapons inspector Hans Blix for scuppering diplomatic efforts to find a peaceful resolution.
Pressed on whether he had actually considered quitting the Cabinet, rather than support military action, Mr Straw said: "Did I ever think, 'I'm going to resign over this'? No, I didn't. We all have our bottom lines.
"Did I understand the nature of the responsibilities on me? Yes, I did, for sure, and weighed them very heavily. But in the event, I came to the decisions that I came to. I did so very reluctantly, but on what I judged to be the best evidence available at the time."
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