Mr Mandelson, forced to resign after misleading Downing Street about his role in the Hinduja passport affair, says he wants to set the facts straight, not seek revenge.
He told the Independent on Sunday that nothing he does "will ever be designed to harm the government or the party".
Mr Mandelson vowed to "co-operate fully" with the independent probe into the passport saga set up by Prime Minister Tony Blair.
Sir Anthony Hammond QC, is leading the inquiry into the passport application by Srichand Hinduja, part of the Hinduja Foundation, which donated £1m towards the Millennium Dome's Faith Zone.
Mr Mandelson resigned after it emerged he misled government colleagues over whether he had asked a fellow minister if a passport application could be reconsidered from Mr Hinduja.
In his defence, Mr Mandelson points to a memo written by a Northern Ireland official, a fortnight before his resignation, which questioned whether the Home Office minister Mike O'Brien could remember the disputed telephone call.
The Independent on Sunday quotes the memo as saying: "I am told you raised the issue with Mike O'Brien in a telephone call or personal note. Mike O'Brien doesn't remember how you raised it."
Mr Mandelson has been out of the country for the past week and is expected to return to Britain and visit his Hartlepool constituency later this week.
He is reported to have recruited another high profile supporter to champion his cause.
Vaz 'won't quit'
Former BBC chief Lord Birt, Mr Blair's Crime Czar, is believed to have pleaded Mr Mandelson's case at Downing Street.
Best selling author Robert Harris had already publicly defended his close friend last week.
Downing Street refused to comment on reports that Lord Birt had spoken up in support of Mr Mandelson.
The Labour Party has also denied newspaper reports suggesting that election donations to the Minister for Europe Keith Vaz, also caught up in the affair, were missing.
It said all the money had been accounted for and the story was inaccurate and denied other reports that Mr Vaz was thinking about quitting as a minister after becoming caught up in the affair.