Geraldine Finucane said the document was "not the truth" just hours after David Cameron apologised for what he said were "shocking" levels of collusion by the security services.
The Prime Minister also raised the prospect of further prosecutions in the case as he laid out the extent of the involvement of agents of the British state in the murder.
One man has been convicted of the crime but last night the Chief Constable of Northern Ireland, Matt Baggott, announced plans to discuss the report, by Sir Desmond de Silva, QC, with the Public Prosecution Service to see if others can be held to account for the murder.
Mrs Finucane renewed her call for a full independent public inquiry into her husband's murder in 1989.
She accused the British Government of suppressing the truth by attempting to blame the dead, as well as now defunct organisations, while exonerating ministers, serving officers and existing security agencies.
Mrs Finucane said: "At every turn it is clear this report has done exactly what was required: To give the benefit of the doubt to the state, its Cabinet and ministers, to the Army, to the intelligence services and to itself.
"The dirt has been swept under the carpet without any serious attempt to lift the lid on what really happened to Pat and so many others.
"This report is a sham, this report is a whitewash, this report is a confidence trick dressed up as independent scrutiny and given invisible clothes of reliability. But most of all, most hurtful and insulting of all, this report is not the truth." Earlier, Mr Cameron had told MPs he was "deeply sorry" for the extent of collusion in the murder.
The British state had "actively furthered and facilitated the murder", he told the Commons.
The report suggested that Mr Finucane's killing might never have taken place had it not been for that involvement, he added.
And Mr Finucane's death could have been prevented had others acted on intelligence they received. Mr Cameron said: "It is really shocking this happened in our country."
The 500-page de Silva review was ordered last October after the Government accepted there had been collusion between Loyalist paramilitaries and the British security forces.
Mr Cameron said there were a series of collusions in the murder of Mr Finucane, who was eating dinner with his wife and young family. These included identifying, targeting and murdering Mr Finucane, he said, as well as supplying a weapon and facilitating its later disappearance.
Agents of the state also "deliberately obstructed sub-sequent investigations."
Although the report found ministers had not been involved, Mr Cameron said they may have been wrongly advised by the security services.
Mr Cameron said that while Sir Desmond's report rejected any state conspiracy "he does find, quite frankly, shocking levels of state collusion".
"He is, and I quote, left in significant doubt as to whether Patrick Finucane would have been murdered by the Ulster Defence Association in February 1989 had it not been for the different strands of involvement by elements of the state."
Labour said it supported the Finucane family in their call for a full public inquiry.
Leader Ed Miliband told MPs: "All sides of the House believe we must establish the full and tested truth about Pat Finucane's murder. But on this side of the House we continue to believe a public inquiry is necessary for his family and Northern Ireland."
Sir Desmond was critical of a defunct Army intelligence unit and the Royal Ulster Constabulary's Special Branch, which each ran at least one agent inside the UDA that had a direct involvement in the murder.
He found that instead of pursuing another loyalist suspect, Special Branch actually recruited him as an agent as well.
Sir Desmond said there was also widespread leaking of sensitive intelligence to loyalists by the security forces during this period of the Troubles – a total of 270 separate leaks in Belfast between 1987 and 1989.
He also accused elements of the security forces of actively attempting to thwart the investigation of Mr Finucane's murder.
Loyalist Ken Barrett was convicted of murder in 2004.