The former political journalist is one of the first high profile members of Blair's inner circle to attend the inquiry.
Campbell will be questioned in relation to his time as director of communications and strategy to the prime minister between 2001 and 2003.
The inquiry is looking at UK policy during the run-up to the 2003 war and after combat had begun.
Campbell is expected to be asked about the compilation of the Government's dossier on Iraq's alleged weapons of mass destruction.
Campbell quit in August 2003 as Blair's press chief during the Hutton inquiry.
Campbell, a former political editor of the Daily Mirror, was Blair's press secretary from 1994 to 2003.
Blair will give evidence at the inquiry later this month.
The final report on the inquiry is expected to be published next year.