Labour and the Greens say their relationship is robust enough to withstand any policy disagreements.
They already have at least one clear division - over whether or not New Zealand should remain in the Five Eyes intelligence network.
In a symbolic move, Labour and the Greens launched their election year campaigns with their first joint State of the Nation event in Auckland today.
Speeches by Labour leader Andrew Little and Greens co-leader Metiria Turei contained no new policy, but sent a message to voters the two parties will work closely this year.
Mr Little was asked if New Zealand should stay in Five Eyes after comments made by the US President Donald Trump about sanctioning the torture of terror suspects.
He said Labour supported staying in the network, and that had not changed under Mr Trump's presidency.
"Five Eyes is about getting information that helps with the security of our nation.
"New Zealanders care about making sure they're safe and secure."
Ms Turei said the Greens had always opposed New Zealand's involvement. Their view remained unchanged.
"We've had different views on this for many, many years and you don't expect other parties to have exactly the same policy and on this.
"We disagree, that's perfectly fine, we can still work together to change the government."
Mr Little said no decisions have been made about electorate deals with the Greens in seats such as Ohariu and Auckland Central, but discussions were under way.
He said he had talked to the former Police Association President Greg O'Connor about a possible candidacy.
Mr Little would not comment about whether Mr O'Connor could stand in Ohariu - a seat currently held by the leader of one of National's support partners, United Future's Peter Dunne.
"I've known Greg for a long time and I've spoken to him myself, more recently... They were conversations, but I talk to a lot of people and most people want those conversations to be kept within the spirit of what they take place, which is, you know, a sounding out, showing an interest - and that's kind of as far as it's got."
Housing, jobs top priorities
In their State of the Nation speeches, both Mr Little and Ms Turei emphasised the "shared values" of the two parties, while launching an attack on the National-led government and new Prime Minister Bill English.
While introducing the speakers, comedian Guy Williams talked about politics overseas and the "man who shall not be named"; then asked the interpreter for the deaf to show the audience how to sign Donald Trump - she obliged with a flick of the hand at her forehead (denoting a certain infamous hairstyle).
To an audience of about 300 to 400 Labour and Green supporters in a hall in Mt Albert, Mr Little talked about his personal battle with cancer.
"It made me think about seizing opportunities; about making the best of this life.
"My battle with cancer colours everything I see, even today."
Mr Little laid out his party's campaign priorities of jobs, affordable housing and a better standard of living.
He alluded to politics in the United States, saying with "President Trump in the US, and the Far Right in Europe - holding onto a positive, inclusive vision is more important than ever".
Mr Little criticised Mr English, calling him a "competent bean counter" and saying since taking office he had "failed the first tests of leadership" by refusing to commit to fighting harder to reduce poverty, or solve the housing crisis.
He said Mr English should front up in Waitangi next weekend, and that he should have sacked his friend and Cabinet colleague Nick Smith in last year's reshuffle.
Ms Turei acknowledged the former party co-leader Jeanette Fitzsimons for her environmental campaigns and the battles of the late Helen Kelly for employee rights.
She talked about the walk out in Parliament last year by female Green and Labour MPs in response to accusations by then-Prime Minister Jon Key that opposition MPs were "backing the rapists" during a debate over New Zealanders held in detention in Australia.
"That was a moment when our parties stood together and stood up for our values.
"I don't need to ask the values of the people here. Or to look up feminism in the dictionary, unlike Bill English.
"I don't need to ask whose side we're on."