The reshuffle is partly driven by Speaker Lockwood Smith's departure to take up the High Commissioner's role in London.
Speaking to One News, Mr Key said the return of Dr Smith to the Cabinet and the appointment of Primary Industries and Local Government Minister David Carter as Speaker were "pretty well-educated guesses".
Mr Key said Ms Adams was safe in her environment portfolio which she assumed when Dr Smith resigned from the Cabinet and also indicated further roles might be in store for her.
"She is someone that's really starting to move up the ranks in terms of our confidence and our sense of how good she could be as a minister."
Mr Key has already indicated that beleaguered Education Minister Hekia Parata is likely to retain that portfolio for the time being.
Green Party co-leader Metiria Turei and NZ First leader Winston Peters both said Dr Smith should not return to the Cabinet as he had acted too unethically and made too many mistakes.
Dr Smith told the Herald he had no knowledge of what the reshuffle held for him but said: "I'd be delighted if the Prime Minister sees fit for me to return to Cabinet.
"The Cabinet is the engine room of Government and any politician that wants to have influence is ambitious to move there."
Meanwhile, Mr Key also said his state of the nation speech on Friday would set out the Government's intention to move forward quickly on economic initiatives that will drive jobs growth.
"We are going to have a sense of urgency about some of the things we're doing and we're putting people, including our political opponents, on notice that yeah, the Government's going to move and act this year and there's an underlying reason for that and that's to ensure New Zealanders have confidence that they're going to have employment to move forward."