Sir John Chilcot is to face questions from MPs amid criticism of delays to his report into the Iraq war.
The inquiry chairman will appear before the Foreign Affairs Committee to discuss the process and “obstacles which remain”.
Prime Minister David Cameron has been among those expressing frustration that the report has yet to be finalised, more than five years after the probe was launched.
The inquiry took evidence from its last witness in 2011 — but Sir John has confirmed its task will not now be completed until after the general election.
Last week MPs debated the delays in Parliament — with some demanding the existing text and key evidence be handed over immediately for publication.
In a letter to Mr Cameron last month, Sir John explained that individuals criticised in the draft document were still being contacted so they have an opportunity to respond — a procedure known as Maxwellisation.
He also said Cabinet Secretary Sir Jeremy Heywood had agreed to the publication of 29 memos from Tony Blair to then US president George Bush, with a “very small number of redactions”, and along with material relating to conversations between the leaders.
But Sir John said there was “no realistic prospect” of delivering the report before May 7.
A statement on the inquiry website has made clear that Sir John does not want to say “anything about the substance” of its work, discuss its “private internal processes” or give further details about Maxwellisation.
He will also not speculate further on possible dates for the publication of the report.
Sir John said: “My colleagues and I have served as members of this Inquiry longer than any of us expected would be necessary.
“But the inquiry has been given the task of examining all of the significant aspects of the UK’s involvement in Iraq over a period of nine years.
“The issues the inquiry is considering are complex and controversial. To ensure that the conclusions we reach are well-founded, it is essential that our approach should be rigorous and comprehensive.
“We are conscious of our responsibility — to the public and to all those whose lives have been deeply affected by the events we are examining — to discharge our duty thoroughly, impartially and fairly.”