Labour MP David Shearer is poised to resign from Parliament to take up the tough job of leading the United Nations' mission in war-torn South Sudan.
The latest political bombshell will mean a byelection in his Mt Albert electorate early next year, the first electoral challenge for the new Prime Minister.
A recommendation for his appointment has been put before the UN Security Council in New York by outgoing UN Secretary-General Ban Ki Moon.
Once approved this week, Shearer will work alongside the commander of 18,000 peace-keepers, with a budget of about $1 billion.
Any of the Security Council's 15 members has two days to object, but given Shearer's previous experience as a senior UN leader in trouble-spots, he is likely to be accepted.
Shearer released a statement this morning saying the Security Council would be making a decision on the post.
"There has been a high degree of media interest in New Zealand about a possible post with the United Nations," he said.
"My name has been proposed to the United Nations Secretary General to be his Special Representative in South Sudan.
"The matter is currently before the Security Council for its decision.
"Until the Security Council completes its consideration of the appointment I will not be commenting further."
The appointment is a personal one by the UN Secretary-General. It is not one that required a nomination by the Government.
But Foreign Affairs Minister Murray McCully said Shearer, who is Labour's foreign affairs spokesman, had the strong support of the Government.
"It is a huge deal," he said.
"[Security Council members have] a couple of days to raise any concerns, so it is not a done deal yet.
"But it is a big feather in his cap.
"This is the toughest peace-keeping assignment on the planet. It is a difficult and dangerous place."
Labour Leader Andrew Little said Shearer had kep him "fully informed about this opportunity and we are very excited for him."
"Should he be confirmed, David will be the only New Zealander in charge of a UN peacekeeping mission. This is a very exciting opportunity for him to make a difference and help bring peace to a country of nine million people torn apart by civil war.
"We fully understand his reasons. This is a once-in-a-lifetime opportunity to take up a senior position at the United Nations which reports directly to the Secretary General."
The three-year civil war in South Sudan has forced more than two million people to flee their homes.
The UN human rights commission last week said ethnic cleansing was taking place and the stage was being set for a repeat of what happened in Rwanda in 1994, when 800,000 mainly Tutsis were killed in three months.
Shearer, a former New Zealand Herald New Zealander of the Year because of his aid work, has previously worked for the UN in conflict zones including Rwanda, Somalia, Iraq, Afghanistan, Kosovo, Lebanon and Liberia.
Shearer was elected to Parliament in a byelection in 2009, replacing former Prime Minister Helen Clark, who is now head of the United Nations Development Programme.
He became Labour Party leader in 2011, after Phil Goff's election defeat, but resigned before a scheduled no-confidence motion by the caucus and was replaced by David Cunliffe.
There was concern at polling under Shearer, which was about mid 30s, but it has never bettered that since and is now in the late 20s.
A byelection in Mt Albert will be the second for Labour to defend, following last weekend's success in keeping Mt Roskill. Shearer won Mt Albert in 2014 with a 10,656 majority.
But like Mt Roskill, National polled higher than Labour in the party vote, by 3536 votes.
A Mt Albert byelection could open the door for Labour's Auckland Central candidate Jacinda Ardern to stand for a safe Labour seat.
Ardern has twice run and lost against National MP Nikki Kaye in Auckland Central, losing by just 600 votes in 2014. Ardern could not be reached for comment this morning.
Following John Key's resignation on Monday, the new Prime Minister will be elected next Monday by the National Party caucus, with Deputy Prime Minister Bill English the front-runner.
Byelections generally cost about $1 million, according to the Electoral Commission.
In the past two years there have been two byelections, one in Northland when Mike Sabin resigned as National MP and in Mt Roskill when Goff resigned after being elected mayor of Auckland.