It is also understood that National would have been happy to give Peters Foreign Affairs as well - although specific portfolios were not negotiated before he announced last Thursday his party was backing Labour.
Ministerial numbers have already been agreed: Labour 16 in cabinet and five outside; New Zealand First, four inside cabinet and one under-secretary; and the Greens, three ministers outside cabinet and one undersecretary.
In a separate ceremony today, Ardern will sign a confidence and supply deal with Green Party leader James Shaw which will set out their policy agreements and portfolios which include Climate Change, to be held by Shaw, and Conservation, to be held by Eugenie Sage.
It is likely Grant Roberton will be finance minister in the new government, Fairfax reports.
It tipped David Parker to have the role of attorney general, Nanaia Mahuta Maori development, deputy leader Kelvin Davis corrections and other portfolios while Ardern's role as PM will also include overseeing intelligence and security and involvement in children and arts.
NZ First deputy leader Ron Mark is expected to pick up the defence role in the new government, it said. Tracey Martin is tipped for a role in the education area while other portfolios for Peters' party are expected to be in economic development and forestry.
Today may be the first day that Winston Peters and James Shaw meet since the election. Shaw has said he would like a sit down with Peters at some point, but Peters has maintained a distance.
Labour conducted separate negotiations with New Zealand First and the Greens and had to ensure that both sets of agreements were compatible.
Some details of the deals have emerged since Thursday but today is the first day the agreements will be published.
Ardern spent the weekend putting the finishing touches on the two agreements to be released today.
She also took a phone call from United States President Donald Trump who congratulated her on the outcome of the election - she and ministers will be sworn in at Government House on Thursday.
She said he had been genuinely interested in our election and spoke about the coverage it had received in Washington DC.
"We are likely to meet at Apec [in Vietnam in three weeks] where I look forward to carrying on talks around our role in the Asia Pacific region, and our commitment to a strong relationship with the United States."
Peters refused to give any hint last night of what portfolio he would get in an interview with Newstalk ZB.
But when asked about his party's choice, he said there was no regret.
"You can't have moments of regret. You've got to know beforehand, no matter what the outcome was going to be, once you've made up your mind ... you've got to endure the experience and hope it will be for the best outcome possible and go the distance and that's what our intention is.
"When we shake hands on this deal we are going to keep our word and I'm positive about the other side doing the same.
"When you look at the circumstances, economically and socially that we are entering this agreement is, there are obviously concerns which we all share. But the point is it was a decision made to ensure that the greatest advantage and least damage would happen to the New Zealand people."
