Peter Dunne will be appointed Minister of Internal Affairs, Associate Minister of Health and Associate Minister of Conservation. Mr Dunne will be a Minister outside Cabinet as he was prior to his resignation in June last year.
Michael Woodhouse will be promoted to the vacancy in Cabinet, and will retain all of his current responsibilities.
Paula Bennett picks up the role of Minister of Local Government, in addition to her current portfolio responsibilities.
The new Minister outside Cabinet will be Peseta Sam Lotu-liga, who will be appointed Minister of Pacific Island Affairs and Associate Minister of Local Government. Mr Lotu-liga is the MP for Maungakiekie and was first elected to Parliament 2008.
"I want to thank Chris Tremain for his work as a Minister, and previously as Senior Government Whip," Mr Key says.
"Chris will be a real loss to the National caucus when he retires at the election and I wish him well for the future.
"I am pleased to welcome Peter Dunne back as a Minister. We have worked together well in the past, and United Future continues to be a valued partner in government.
"While 2013 brought its challenges, both Peter and I start this election year looking forward, not back."
Mr Key also congratulated Mr Lotu-liga on his elevation to the Ministry.
"Sam has very strong ties with the Pasifika community and has represented their interests in caucus well.
"He is well placed to build on the work that Hekia Parata has done in this portfolio this past term."
The Governor-General will swear in the new Ministers on January 28, before Parliament returns for the new year.