An exciting day for the Green Party.

The Greens have been told which roles they'll have in the next Government, but have to keep the details under wraps until next week.

Leader James Shaw and MP Eugenie Sage, Julie Anne Genter, and Jan Logie will fill four positions in their confidence and supply agreement with the Labour Party.

Three will be ministers and one will be an under-secretary, working alongside a minister.

James Shaw said they're very happy with the roles they've been assigned but can't reveal them until incoming Prime Minister Jacinda Ardern announces her Cabinet next week.

However, he said they're completely consistent with what the party said its priorities were, during the election campaign.

"Given that this is the first time that we will have had ministerial posts in the entire 27 that we have been a political party it is a huge step forward for us."

Shaw said they know which portfolios they'll have, but can't reveal details.

"The Prime Minister has that prerogative and I understand that she is intending to make an announcement about the full cabinet line up including Labour, New Zealand First and Green ministers and under secretaries next week."

The portfolios are thought include Climate Change, Associate Finance, Conservation and the Ministry for Women.