Inquiry chairman John Chilcot said the government commissioned study had heard from about 140 witnesses over the last year.
Following a visit to Iraq, the panel will decide whether to recall witnesses for additional sessions, in cases where there are apparent contradictions in their evidence.
Blair gave evidence to the inquiry in January. Since then, witnesses have questioned parts of his testimony.
The inquiry is examining mistakes made in the build-up to and aftermath of the 2003 U.S.-led invasion.
It won't apportion blame or assign criminal liability, but will issue a report later this year.