Te Atatu MP Chris Carter is leaving New Zealand next Wednesday to take up a position with the United Nations in Afghanistan's capital, Kabul.
His role as a director of the Governance Unit of the UN mission in Kabul will involve battling corruption.
"I will head a team based in the Ministry of the Interior, which advises President Karzai and his ministers on effective ways of improving local governance at the provincial level with the police and the judiciary," he said.
"The UN has a lot of pilot projects in Afghanistan and I will advise New York as to the effectiveness of those."
There will not be a byelection in Te Atatu because the six-month window before the general election has closed. The seat will be left vacant.
He said his contract was for one year, with a possible extension.