A full copy of Robert Mueller’s report into Russian interference in the 2016 US election will be released by mid-April "if not sooner," the attorney general said.
William Barr said the report is "nearly 400 pages" long, without including appendices, and he hopes to make it public in its entirety with some redactions.
In a letter to Congress the attorney general said: "Everyone will soon be able to read it on their own."
Mr Barr said he was willing to appear before the Senate and House judiciary committees to give evidence about the report on May 1 and May 2.
The redactions will include material intelligence agencies consider could compromise sensitive sources and methods, and secret information given to a grand jury.
Mr Trump has the right to assert executive privilege over some material obtained from the White House.
However, Mr Barr said the president had indicated he would "defer to me," and so there were no plans to submit the report to the White House in advance of its publication.
Following an investigation lasting nearly two years Mr Mueller, the special counsel, delivered his report to Mr Barr a week ago.
A few days later Mr Barr released a four-page summary, written by him after reading Mr Mueller’s report.
That summary exonerated Mr Trump, and campaign officials of colluding with Russia.
The summary said Mr Mueller had left unresolved the question of whether Mr Trump obstructed justice during the inquiry.
Mr Barr concluded, based on the evidence presented by Mr Mueller, that it was not sufficient to charge the president with obstruction.
Mr Trump has turned the findings into a political weapon, calling the inquiry "the greatest hoax in the history of our country".
He has warned that those behind the probe "would be held accountable".
Mr Trump said: "This was nothing more than a sinister effort to undermine our historic election victory and to sabotage the will of the American people."