Brooks, who resigned in July as chief executive of News International, Rupert Murdoch's British newspaper division, detailed her close friendships with Cameron, former Prime Minister Tony Blair and their families, in testimony to the country's inquiry into media ethics.
In six hours of questioning, Brooks listed Christmas parties, private dinners and hotel lunches she shared with the country's most powerful political leaders. She also acknowledged that she used her access to lobby the British government over a planned News Corp. takeover deal that would have netted Murdoch's media empire a lucrative satellite broadcaster.
The 43-year-old, a former editor of two Murdoch tabloids — The Sun and the now-defunct News of The World — has twice been arrested and questioned by police about illegal eavesdropping and obstruction of justice. She has not been charged with any offence, but is currently on bail pending further investigations — so the inquiry lawyer did not question her directly about phone hacking allegations.
Known for her striking red curls and meteoric rise from junior employee to top editor at News of the World, Brooks said Cameron was a personal friend and a neighbour in the picturesque Cotswolds area of southern England.
After she quit in July due to the uproar over phone hacking, Brooks said she had received "indirect messages" of support — text messages sent by the aides of politicians, but relaying their personal thoughts — including from Cameron.
"I received some indirect messages from No. 10, No. 11, the Home Office and Foreign Office," Brooks said, referring to Cameron, Treasury chief George Osborne and other leading Cabinet members.
She agreed with inquiry lawyer Robert Jay that a message from Cameron had told her to "keep your head up" and expressed regret that he could not offer more support publicly, because of the political pressure he was under over the hacking scandal.
The message was "along those lines, I don't think they were the exact words," Brooks said.
Brooks said she and Cameron would trade texts at least once a week, or twice a week during busier periods such as Britain's 2010 national election.
"He would sign them off 'DC,'" said Brooks, who showed composure and flashes of humour as she testified. "Occasionally he would sign them off LOL, 'lots of love', until I told him it meant 'laugh out loud.'"
Brooks confirmed that she had discussed tabloid phone hacking with Cameron, including after toxic revelations that the News of the World had hacked murdered schoolgirl Milly Dowler's phone when she disappeared in 2002. The girl was later found dead.
Public revulsion over the hacking of Dowler's phone led Murdoch to shut down the 168-year-old News of the World in July, and saw Cameron set up the ethics inquiry, led by Lord Justice Brian Leveson.
Cameron has previously acknowledged that he has known Brooks' husband Charlie for 30 years and that he had ridden on a retired police horse that had been loaned to Brooks.
She told the inquiry that Blair, his wife and advisers "were a constant presence in my life for many years" and said the ex-leader had also offered support when she quit. Blair was among the political heavyweights who attended her 40th birthday party, hosted at Murdoch's home, she said.
In 2003, as editor of The Sun, Brooks said her newspaper's support for Britain's role in the U.S.-led invasion of Iraq saw their relationship deepen.
"During the Iraq war, I spent more time than usual talking to Tony Blair and Downing Street," she said. Public opinion was divided in Britain over the war, with large numbers opposed to Blair's decision to join the conflict.
Blair's successor Gordon Brown, however, was "incredibly aggressive and angry" after The Sun ditched its support for his Labour Party before Britain's 2010 election — which Brown lost. As other politicians sent texts after she quit, Brown "was probably getting the bunting (banners) out," Brooks joked with a smile.
His wife Sarah Brown, however, was part of a social circle that also included Brooks, Elisabeth Murdoch — Murdoch's daughter — and Wendi Deng, Murdoch's wife.
However, Brooks insisted politicians did not court her in an effort to get closer to Murdoch.
Evidence from Brooks raised new doubts over Culture Secretary Jeremy Hunt's handling of a decision on whether News Corp. should be authorized to take full control of British Sky Broadcasting, a satellite broadcaster in which Murdoch's company already holds a 39 per cent stake.
Hunt had been supposed to be acting as an impartial judge to decide whether to approve the takeover or refer it to regulators. But the ethics inquiry previously published 163 emails sent by News Corp. lobbyist Frederic Michel which alleged that either Hunt or his office had leaked sensitive information to Murdoch's company and had indicated their support of the News Corp. takeover case.
An adviser to Hunt has since resigned.
Brooks said in one email she had received, Michel claimed that Hunt had "asked me to advise him privately in the coming weeks and guide his and No.10's (Cameron's office) positioning."
However, she acknowledged she believed the lobbyist sometimes exaggerated. Hunt's office said he "behaved with integrity on every issue."
Murdoch dropped the takeover bid for BSkyB in mid-2011, after the furor over phone hacking.
Hunt is scheduled to give evidence to the inquiry at a later date.