Labour MP Charles Chauvel is resigning from Parliament to take up a position with the United Nations in New York.
Mr Chauvel entered Parliament as a list MP in 2006.
Mr Chauvel said he has accepted a position with the UN advising on parliamentary development and democratic governance and is looking forward to the new challenge.
The MP said he regrets that he will not be able to be part of a future Labour government, but the opportunity is too good to miss.
"I've learnt a lot in the job. I've had some extraordinarily generous companions, friends and colleagues in this place, and I wouldn't have missed the experience of the last six-and-a-half years at all."
Leader David Shearer said on Tuesday he envisaged Mr Chauvel taking a senior role in a future Labour government and admits the departure is concerning.
"Personally, I'm very sorry that Charles is going because his expertise in the justice area is without equal in our Parliament, let alone in our party ... but on the other hand, this is a great opportunity for him and good on him for reaching out and taking it."
Charles Chauvel's last day at Parliament will be 11 March.