Senior civil servant Sue Gray has delivered her completed report into Downing Street lockdown parties to the prime minister.
The final report - which is 37 pages long plus photos - had been delayed by the Met police inquiry that ended last week.
An interim version, released in January, criticised leadership within No 10.
It added that some events in government offices should not have taken place.
The government has confirmed Prime Minister Boris Johnson will give a statement to the Commons later.
He is currently reading a print out of the report, as he prepares to face Labour leader Sir Keir Starmer at PMQs at 12.30 BST.
Ms Gray contacted senior civil servants she intends to name in her final report over the weekend. It is understood the report has pictures of the PM, Chancellor Rishi Sunak and Cabinet Secretary Simon Case.
BBC political editor Chris Mason says Mr Case, the UK's most senior civil servant, is not resigning and will not be sacked.
And our political editor says that the prime minister is expected to tell the Commons that he commissioned the report to set the record straight and "allow us all to move on".
Mr Johnson is likely to add: "I accept full responsibility for my failings. I am humbled by the whole experience. We have learned our lesson."
Publication of Ms Gray's report comes after further revelations in recent days about gatherings held in Downing Street during lockdown, with photos of the PM raising a glass at a leaving do leaked to ITV and insiders revealing the extent of the gatherings to the BBC's Laura Kuenssberg.
In a BBC Panorama report, people who attended the events told of how staff crowded together and sat on each other's laps and how party debris was left out overnight.
The insiders also said parties went on so late that, on occasion, some ended up staying in Downing Street all night, and that staff mocked others who tried to stop what was going on.
The revelations have sparked fresh claims from opposition MPs and others that Mr Johnson knowingly misled Parliament when he previously told the Commons no Covid rules had been broken in Downing Street.
There have also been calls for the Metropolitan Police to explain why Mr Johnson did not receive a fine for attending the leaving do, when at least one person at the event was fined.
Speaking ahead of the report's publication, Environment Secretary George Eustice said he "absolutely acknowledges" public feeling adding: "It's not just the optics, it's understandable that people will feel anger because there were instances where people couldn't attend funerals of close friends, couldn't visit loved ones."
Plenty of Conservative MPs acknowledge privately the revelations of the last six months have permanently damaged the prime minister's reputation in the eyes of many.
His character, his judgement, his integrity. Bluntly, whether he tells the truth.
The government is braced for a difficult day.
But the volcanic anger of many Tory MPs just a few months ago has cooled; their appetite for revolution, replacing him, significantly dimmed.
What led to Gray report?
No 10 appointed the UK's top civil servant, Simon Case, to lead an inquiry into gatherings held in Downing Street and Whitehall during the pandemic after a raft of allegations emerged at the end of last year.
However, he was forced to step aside in December after it was revealed a party took place in his own office.
Ms Gray took on the job, examining 16 events over a dozen dates between May 2020 and April 2021.
But her report was delayed in January when the Metropolitan Police launched its own investigation into 12 of the gatherings.
An interim report published by Ms Gray, days later, pointed to "failures of leadership and judgement" by parts of No 10 and the Cabinet Office.
But now the Met has completed its investigation - which resulted in 126 fines, including one for the prime minister for attending a birthday party - Ms Gray can publish her full findings.
As well as his appearance in the Commons, the prime minister will face a meeting of the Tory backbench 1922 committee in the afternoon.
Mr Johnson has managed to keep the support of the majority of his party so far, but many Conservatives have said they were waiting to read Ms Gray's full report before deciding on his future as their leader.
Tory MP Charles Walker told the BBC that the report would "make uncomfortable reading", but the "seminal moment" for the PM had been when the police report concluded and he faced no more fines.
"My suspicion is - actually my strong inclination is - the prime minister is through the worst of it," he added.
Fellow Tory MP Stuart Anderson also said: "People have moved on from this."
Asked if he was nervous of the report, he added: "I'll be glad when it's done. Nobody wants to be in this scenario, but let's get it done and move forward."
Others have been more critical since the revelations, however, with former Justice Secretary Sir Robert Buckland saying Mr Johnson will have to resign if he knowingly misled Parliament.
He told BBC Radio Wiltshire: "Legitimate questions have to be raised, and that's why I want to see the fullest explanation."
How were you and your family affected by the pandemic? Email firstname.lastname@example.org.
Please include a contact number if you are willing to speak to a BBC journalist. You can also get in touch in the following ways: