The former director of communications denied a BBC report that he "sexed up" a dossier claiming Iraq could launch a chemical or biological attack within 45 minutes, to help justify the war.
Dr David Kelly, the UK ministry of defence weapons expert, believed he may have been the source of the BBC's story, and officials confirmed his name as such to some reporters.
Kelly was found dead near his home with slashed wrists soon afterwards.
Campbell resigned in August 2003, a month after Kelly's suicide, insisting he had decided to resign to spend more time with his family well before Kelly's death.
An official inquiry subsequently exonerated him over the affair.
Blair will give evidence sometime in the two-week period from January 25. Public interest is so great that a ballot is being held for seats.
The former prime minister faced a major backlash in Britain over the decision to support former US president George Bush over the war.
Blair insisted last month he would have supported the war, which did not get United Nations approval, even if he had known Iraq did not have weapons of mass destruction.
He resigned in 2007, having led his Labour party to three election wins.
The inquiry, which started hearing testimony in late November, has faced criticism that it is not questioning witnesses rigorously enough.
Critics of the invasion had long demanded an investigation into whether the war, which was extremely unpopular in Britain, was illegal.
Many were disappointed when it was announced that the inquiry had no power to apportion blame or establish criminal or civil liability.