In a dramatic move, lawyers have secured "core participant" status at the hearings for the Prime Minister and seven members of his Cabinet.
It marks a sea-change in the UK Government's involvement with the inquiry, set up by Mr Cameron at the height of the phone hacking scandal last year.
The decision is designed to avoid a re-run of last week, when ministers were surprised by explosive evidence of contact between Culture Secretary Jeremy Hunt's department and the Murdoch empire.
Now UK ministers, including Mr Hunt, will have access to witness statements in advance.
The development comes just days before Mrs Brooks, a former editor of the Sun, and Andy Coulson, Mr Cameron's former communications chief, are due to give evidence.
There has been speculation their testimony could prove embarrassing for the Prime Minister and even potentially derail the Coalition's efforts to use next week's Queen's Speech to draw a line under weeks of negative headlines and accusations of "omnishambles".
Mr Cameron is under pressure to release details of emails and text messages between himself and Mrs Brooks, who also edited the News of the World, amid accusations their relationship was "too chummy".
The Conservative leader has already faced embarrassment over his admission he rode a horse loaned to Mrs Brooks by Scotland Yard.
He has also faced questions over his decision to hire Mr Coulson, who edited the News of the World when its royal editor was convicted of phone hacking.
The UK Government's decision to apply for a role within the inquiry yesterday was unexpected. Most of those who have been granted core participant status made their applications months ago.
Even Lord Justice Leveson described the Coalition's submission as "late" during an emergency session of the inquiry to announce his decision.
Among others granted the status were Deputy Prime Minister Nick Clegg and his Liberal Democrat colleague Vince Cable, who once declared he intended to wage war on the Murdochs to undercover reporters.
Tory Cabinet ministers given access to confidential documents include Justice Secretary Ken Clarke, Home Secretary Theresa May, Education Secretary Michael Gove and Chancellor George Osborne. All, apart from Mr Osborne, are due to give evidence in person to the inquiry over the coming weeks.
From Monday, Lord Justice Leveson will probe allegations that senior politicians were too close to newspaper proprietors including the Murdochs and their executives.
Concern over the access newspaper moguls appeared to have to senior politicians led in part to Mr Cameron's decision to set up the Leveson Inquiry.
However, until now he has kept his distance, despite agreeing to appear as a witness.
It was also reported yesterday that the Conservative leader is receiving training before his appearance.
The Government is still facing calls for Mr Hunt to resign after last week's revelations.
Details released by the inquiry showed contact between his office and a senior executive at Rupert Murdoch's News Corporation.
Within 24 hours his special adviser Adam Smith had quit, admitting he had gone "too far" in his contacts with News Corp.