MATT MCCARTEN: He has a reputation as an organiser, negotiator and a party "hard man".

Labour leader David Cunliffe has confirmed former Alliance president Matt McCarten will be his new chief of staff.

McCarten said the two had not known each other before the past few weeks but there was an "extraordinary chemistry" between them.

He said he was pleasantly surprised at the direction Cunliffe was taking Labour.

Announcing the appointment this afternoon, Cunliffe said McCarten had a distinguished career of service to unions and progressive causes.

"Matt is one of the country's pre-eminent political strategists on the Left-hand side of politics," he said.

While McCarten would co-ordinate his office, Cunliffe also announced David Talbot, from Labour pollster UMR Research, would head the party's election campaign.

McCarten said advocating for those at the bottom of the pile was his life's work, and that Cunliffe had given those people hope.

"We have a lot of similar beliefs and I just thought this man could be the prime minister and should be the prime minister, and anything I could do to help a Labour-led Government under MMP I will do," he said.

McCarten said his health now was good and he had "the all clear" from cancer. He had been diagnosed with what he was told was terminal cancer four years ago and at one stage thought he had only a few months to live.

He said he now had "unfinished business". He had told the United union executive last night about his new role.

McCarten, who split acrimoniously from former Alliance leader Jim Anderton, said the two would work together on the election campaign but dodged questions about whether the two had now reconciled.

Anderton ran Labour's campaign in the Christchurch East by-election bringing to a close a division between him and Labour going back to the 1980s..

McCarten said that if Labour had been the party it is now when he left in 1989, he would never have quit and the New Labour Party - later part of the Alliance - would not have existed.

Asked about his support for various parties over time, including the Maori Party and Mana, McCarten said he would put his loyalty to working class values and would put the labour movement up against anyone anytime.

"I fight for rights of people," he said.

McCarten said he would support initiatives he thought moved things forward.

He said the key to unity in the Labour caucus was having a common cause, but he did not have an insider's knowledge of the caucus.

Prime Minister John Key said the appointment showed Labour was "going careering off to the Left", and the unions were getting an even tighter grip on the Labour Party.

"He [McCarten] is hard-Left," Key said.