Counselling would be free for anyone under 25 in a Green government, leader James Shaw says.
The party has launched its youth mental health policy targeting New Zealand's youth suicide rate, which is among the highest in the world.
The counselling services, costed at $116 million a year, would be part of the Green Party's planned $263 million annual boost to youth mental health services.
"We also want to work towards introducing that for all adults as well over time," Mr Shaw said.
"Clearly, given New Zealand's appalling statistics when it comes to youth suicides that is the area where we need to make the greatest intervention."
The plan also includes $100 million additional spending on youth mental health services to work alongside the counselling, which would be a preventative measure.
"If they need to move into the health system (we need to ensure) that the health service actually has the staffing and the beds available for people then they need to move into that level of care."
A third component would reduce the ratio of school counsellors from one per 800 students to one for every 400 students, and ensure all the counsellors are professionally trained.
The Mental Health Commission and an inquiry into mental health services would be held.
"Services are patchy around New Zealand," Mr Shaw said.
"We actually feel that it is well past time that there is a full public inquiry into the resourcing of our national health services in New Zealand."
The Public Services Association, which represents mental health workers, has welcomed the plan.