Mr Finucane was shot dead by UDA/UFF gunmen at his north Belfast home in 1989. Allegations of collusion between security forces and loyalists surrounded the murder of the 38-year-old.
The 500-page report, headed up by Sir Desmond de Silva QC, was ordered by Mr Cameron in October last year and was published on Wednesday.
It found state employees actively furthered and facilitated the killing.
Speaking at the House of Commons, the Prime Minister said the murder was an "appalling crime" that happened during an "extremely dark and violent time in Northern Ireland's history".
He said the review found that the Army and Special Branch had advance notice of a series of planned UDA assassinations, but took no action.
"It should have been clear to the RUC Special Branch from the threat intelligence that... the UDA were about to mount an imminent attack but... it is clear that they took no action whatsoever to act on the threat intelligence," Mr Cameron said of Mr Finucane's murder.
The whole country is entitled to know the extent and the nature of collusion, and the extent of the failure of our state and government.
The de Silva report found that employees and agents of the state played "key roles" in the murder, and Mr Cameron said: "It cannot be argued that these were rogue agents."
The Prime Minister added: "Sir Desmond says he is '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'."
But the de Silva review found no evidence that any government minister was aware in advance of the murder or knew about the subsequent cover-up.
Mr Cameron described the degree of collusion exposed as "unacceptable" and apologised to the Finucane family.
"I am deeply sorry," he said, adding that the Finucanes had suffered "the most grievous wrongs".
The family did not participate in Sir Desmond's report, which cost £1.5m to complete.
The Prime Minister said that Sir Desmond had "full and unrestricted access to government papers", including previously classified documents. He added that the author's decision over what to publish was "entirely his own".
We must, as the United Kingdom, accept that sometimes our state did not meet the high standards we set ourselves during the Northern Ireland conflict.
Leader of the Opposition, Ed Miliband, said that the de Silva report made for "disturbing and uncomfortable reading".
He added that he "respectfully disagreed" with the Prime Minister when it came to the issue of a public inquiry, which had been sought by the Finucane family but refused by David Cameron - who believes that it would not produce a fuller picture of what happened.
"The past is painful and often difficult, but we must establish the full and tested truth about Pat Finucane's murder," Mr Miliband said.
Vernon Coaker, Shadow Secretary of State for Northern Ireland, said that peace and progress could not be taken for granted.
"A proper investigation into the murder of Pat Finucane, and the circumstances surrounding it, is fundamental to the agreements made between the two governments," he said.
"The findings of this report are shocking and appalling. They provide a step in getting to the truth, but cannot provide the whole truth. Only a public inquiry will do that."
Chief Constable Matt Baggott apologised to the Finucane family on behalf of the Police Service for the "relentless attempt to defeat the ends of justice". He added that he would be meeting with the Police Ombudsman and PPS to discuss the findings.
He expressed disappointment at "how the Finucane family were so badly and abjectly failed".
"This failure has done a great disservice to the bravery and dedication of the many who joined the police to keep all communities safe throughout the awfulness of those difficult times," he said.
"Today, like any Police Service, we cannot prevent crime without the use of intelligence. But today, the PSNI operates within a framework of independent scrutiny and regulation that is both rigorous and demanding.
"We are determined to keep everybody safe and uphold their human rights."
The information provided by Desmond de Silva is a damning indictment of British state collusion in the murder of citizens.
Sinn Féin President Gerry Adams said that the de Silva review confirms collusion, but "everybody already knew this".
"David Cameron today sought to use the review as a pretext for denying the family a public inquiry - a commitment that was made by the British government at Weston Park in 2001," he added.
"It reveals some of the extent to which this existed. It does not diminish the need for a public inquiry."
SDLP leader Alasdair McDonnell said the findings of the de Silva report "fall far short".
"It confirms that the UDA was steered and prompted to murder Pat Finucane by members of the RUC special branch," the south Belfast MP said.
Dr McDonnell said his party continues to support the Finucane family request for a public inquiry.
"We feel that we've still only got half the truth," he commented.
The DUP MP for North Belfast Nigel Dodds said: "It is right that the Prime Minister has stood against holding a public inquiry in this situation because of the message that would send out to countless other victims, many of whom have seen little or nothing done to investigate crimes which still affect them today."
Meanwhile a statement by the UUP said: "We acknowledge the loss and suffering of the Finucane family. We also acknowledge the loss and suffering of all families, and equally as importantly, the living victims.
"The Ulster Unionist Party calls on the Secretary of State to consider urgently how to end this disjointed, piecemeal approach to dealing with the past, and convene talks to discuss an inclusive and comprehensive way forward."