Kiwis will be asked to vote on whether the law surrounding the personal use of cannabis should be changed.
The Green Party has secured the referendum as part of its deal with the incoming Labour-led Government.
An email sent to Green Party delegates and detailing policy gains includes "Increase funding for alcohol and drug addiction services and ensure drug use is treated as a health issue and have a referendum on legalising the personal use of cannabis at, or by, the 2020 general election.".
The Greens campaigned on making cannabis legal for personal use, including possession and cultivation, with a legal age limit for personal use.
They want to assess evidence from overseas jurisdictions with legal cannabis is sold to determine the best model for New Zealand.
"While waiting for broader law change for cannabis, remove penalties for any person with a terminal illness, chronic or debilitating condition to cultivate, possess or use cannabis and/or cannabis products for therapeutic purposes, with the support of a registered medical practitioner", the policy said.
Other policy gains outlined in the email to delegates included "free counselling for under-25s and access to mental health services and support for everyone" - and also "significant climate action" and "overhaul of the welfare system"