An agreement has been reached over disclosing sensitive documents detailing discussions between Tony Blair and George Bush.
Jeremy Heywood, the British government's most senior civil servant, has agreed the principles of handing over information.
He was principal private secretary to Mr Blair in 10 Downing Street in the run-up to the war in 2003.
The information to be handed over includes 25 notes from Mr Blair to Mr Bush and more than 130 records of conversations between the former British prime minister and the then US President.
John Chilcot's inquiry completed public hearings in 2011, but publication of its report is understood to have been held back by negotiations over the publication of private communications.
Officials said a time has still not been set for the date of publication.
Earlier this week, Mr Blair insisted he was not the reason for the delay in the publication of the Chilcot Inquiry report as demands for its swift release increased.
"It certainly isn't me who is holding it up," he told the BBC. "The sooner it is published the better from my perspective as it allows me to go and make the arguments."
Letters must be sent out to individuals facing criticism in the report before it is published under the "Maxwellisation" process to give them an opportunity to respond.
Once that is complete, the report can be finalised and sent to British Prime Minister David Cameron, who has previously said he hopes it will be published by the end of the year.
A Cabinet Office spokesman said: "The Government is pleased that agreement on a way forward on both Cabinet papers and UK/US exchanges has now been reached with the inquiry.
"This allows for the declassification and publication of the material the inquiry believes it needs to explain its conclusions.
"Resolving this issue has taken longer than originally hoped but these are sensitive issues.
"The UK/US head of government channel is very important and must be handled sensitively.
"The government and the inquiry are working to ensure the inquiry's report is published as soon as possible and the government is doing everything it can to facilitate that."