Rupert Murdoch is expected to reveal discussions with top British politicians when he gives evidence to the Leveson Inquiry on Wednesday.
The 81-year-old media tycoon's appearance comes after his son James's testimony yesterday led to calls for the resignation of Culture Secretary Jeremy Hunt.
The press standards inquiry heard claims that Mr Hunt backed News Corporation's bid to take over BSkyB and leaked inside information to the media giant.
Labour last night called for the Culture Secretary's resignation after the release of a 163-page dossier of emails detailing contacts between his office and senior News Corporation executive Frederic Michel.
Mr Hunt, who said it was "not a time for knee-jerk reactions", later wrote to Lord Justice Leveson asking if his appearance could be brought forward, promising in a statement that his evidence would show the public he had conducted the process "with scrupulous fairness".
Rupert Murdoch, News Corp's chairman and chief executive, faces a two-day grilling under oath.
He will be asked about the phone-hacking scandal, which led to the closure of the 168-year-old News of the World last July after revelations that the paper listened to the voicemails of murdered schoolgirl Milly Dowler.
He will also be questioned about his oversight of his UK newspapers, and whether he exerted undue influence over British public life through his papers and his regular meetings with prime ministers and other leading politicians.
The billionaire told the Commons Culture, Media and Sport Committee last July that he met David Cameron "within days" of the 2010 general election and was invited to Downing Street by Gordon Brown "many times". Tony Blair is godfather to one of his children.
News Corp still owns The Sun, The Times and the Sunday Times, and has a 39% stake in satellite broadcaster BSkyB.
Today will be Mr Murdoch's highest profile public appearance since he gave evidence to MPs last July.
The tycoon told MPs it was the "most humble day" of his life and apologised for the phone-hacking scandal, but the session was disrupted when a protester pelted him with a foam pie.
The Leveson Inquiry has a wide-ranging remit to examine the culture, practices and ethics of the press, and make recommendations for the future regulation of British newspapers.
It has already taken evidence on unethical and possibly illegal behaviour by journalists, and on relations between police and newspapers.
Inquiry chairman Lord Justice Leveson is now turning to contacts between politicians and the national press.
Court 73 at the Royal Courts of Justice in central London is likely to be packed for Mr Murdoch's evidence sessions today and tomorrow.
A small number of seats in the hearing room will be made available to the public on a first come, first served basis but security will be tight to prevent any repeat of the Culture, Media and Sport Committee protest.