Former solicitor-general Michael Heron QC will lead the inquiry into the leaking of National leader Simon Bridges' travel and accommodation expenses to the media.
Parliament's Speaker Trevor Mallard announced the appointment today.
"Mr Heron is experienced in conducting high-profile inquiries relating to integrity and conduct," Mallard said in a statement.
Heron was appointed in consultation with Bridges.
Mallard announced last week that a Queen's Counsel would be appointed to lead the inquiry into who might have given the information to Newshub ahead of its public release last Thursday.