Former deputy prime minister Jim Anderton has died in hospital following a period of ill health.
Mr Anderton, 79, died in Christchurch's Cashmere View Hospital overnight, his widow Carole said in a statement on Sunday.
Funeral details are yet to be announced.
Prime Minister and Labour Party leader Jacinda Ardern says the country has lost a man of integrity, compassion and dedication to public service.
"Jim Anderton devoted much of his adult life to public service and to the ideals of the Labour movement," she said in a statement.
"He was a towering figure in the Labour movement for several decades. He will be remembered as someone who stood up for his principles and for the people he represented. His integrity during difficult times marked him out as a true leader.
"He never gave up on the values of the Labour movement, and worked tirelessly to bring it back together through the years of the fifth Labour-led government.
"A man of deeply-held values and ideals, he was practical and compassionate. We mourn his loss, and extend our heartfelt sympathies to Jim's wife Carole, his family and friends."
Auckland-born Mr Anderton was first elected to public office in 1965 as a Manukau city councillor.
He entered parliament as the Labour MP for the Christchurch electorate of Sydenham in 1984
He famously left the party in 1989 over its Rogernomics policy saying "I didn't leave the Labour Party, the Labour Party left me".
He formed the New Labour party and then led the Alliance party which won 10 seats in the 1999 election.
He was deputy prime minister under Helen Clark between 1999 and 2002 and he then led the Progressive Party when he was MP for Wigram.
Mr Anderton retired from parliament at the 2011 election.
After a failed bid at the Christchurch mayoralty, Mr Anderton became involved in the successful campaign to have the earthquake-damaged ChristChurch Cathedral restored.
Last year, he became a Companion of the New Zealand Order of Merit for his services as an MP.