Former High Court judge Lester Chisholm will conduct a government inquiry into allegations former minister Judith Collins was part of a smear campaign against former Serious Fraud Office boss Adam Feeley.
Collins quit as a minister on Saturday last week after emails dating to 2011 emerged saying she had been "gunning" for Feeley.
The emails said Feeley was the target of a campaign to undermine him by Whale Oil blogger Cameron Slater and Cactus Kate, whose real name is Cathy Odgers.
At the time of the emails, Collins was overseeing the SFO, and the State Services Commission was investigating Feeley's actions.
According to the emails, Mark Hotchin, the former head of collapsed finance group Hanover who was being investigated by the SFO at the time, may have been paying the bloggers, who were also targeting the Financial Markets Authority.
Prime Minister John Key today released the terms of reference of the inquiry as he announced Chisholm's role.
The inquiry is the lowest-level inquiry available under the Inquiries Act, 2013, although under it all inquiries have the same powers.
The probe will inquire into and report on allegations that Collins "was involved in efforts to undermine Mr Feeley during his tenure as director of the Serious Fraud Office".
Specifically it will examine whether Collins acted inconsistently with the conduct expected of a minister, provided information about Feeley to Slater or others who were not entitled to it and whether Collins inappropriately sought or received information about Feeley from Slater or others.
The report will "identify and report on any other issues relevant to the above matters, to the extent necessary to provide a complete report on those matters".
Labour has been calling for a commission of inquiry, while NZ First is demanding a royal commission of inquiry as a condition for coalition talks.
Chisholm, a Companion of the New Zealand Order of Merit and a former member of the New Zealand Law Practitioners' Disciplinary Tribunal, recently chaired the board of inquiry into the Ruataniwha dam and irrigation scheme.
The inquiry is required to report back to the prime minister, whoever that may be, no later than November 28.