Democrats and Republicans alike have clamored to see the final conclusions from the highly guarded investigation.
But like the probe itself, the process of preparing the report for its public rollout has been the subject of intense scrutiny and controversy on Capitol Hill.
Less than two days after receiving the lengthy report, Barr summarized what he said were its main conclusions in a four-page letter to congressional Judiciary Committee leaders.
Barr shared two main conclusions from Mueller's probe, both of which were celebrated by Trump.
The special counsel did not establish conspiracy or coordination between the Trump campaign and the Kremlin, Barr wrote, quoting an excerpt from the report itself.
On the question obstruction, Barr quoted Mueller saying the report "does not conclude that the President committed a crime, [but] it also does not exonerate him."
Mueller's lack of a definitive stance on obstruction left the final decision to Barr and Rosenstein. They concluded: "The evidence developed during the special counsel's investigation is not sufficient to establish that the president committed an obstruction of justice offense."
Both sides of the political aisle were quick to respond that evening.
"No Collusion, No Obstruction, Complete and Total EXONERATION," Trump tweeted, even though he was not exonerated by Mueller.
House Speaker Nancy Pelosi, D-Calif., and Senate Minority Leader Chuck Schumer, D-N.Y., immediately went after Barr's credibility, saying in a statement that the attorney general "is not a neutral observer and is not in a position to make objective determinations about the report."
Some Democrats had voiced concerns that Barr may have pre-judged the Mueller probe in light of an unsolicited memo he sent to the Justice Department last June criticizing the Mueller probe's obstruction inquiry as "fatally misconceived."
In addition, reports from The New York Times and Washington Post citing several members of Mueller's team poured gasoline on the firestorm of controversy following Barr's summary. The team members, speaking on the condition of anonymity, reportedly said that the evidence that Trump tried to obstruct the probe is stronger than Barr has publicly suggested.
Barr holds the ultimate authority on the report's release. He gained oversight responsibilities from Rosenstein, who himself adopted those duties after former DOJ head Jeff Sessions recused himself from any investigations into Russian election meddling.
While Barr has vowed to be as transparent as possible in the handling and release of the report, he has made clear that both Congress and the public will see a version of the report that contains redactions in four areas. The attorney general said the redactions will be color-coded, so that readers can better understand why certain information was hidden.
That material includes information about intelligence sources and methods, details of ongoing investigations and other information that would "unduly infringe on the personal privacy and reputational interests of peripheral third parties."
But the most controversial redaction category involves the DOJ's insistence that information related to Mueller's grand jury cannot be released under federal law. Democratic lawmakers, led by House Judiciary Chairman Jerrold Nadler of New York, have pushed back on that argument, claiming Barr could share that information with Congress if he wanted to.