He said he would prefer to remain off the list, but constitutionally the party leader and deputy had the top two spots.
He was not worried that his new promotion might mean voters would elect Mana leader Hone Harawira as a way of ensuring both got into Parliament.
"I think people will see that here's an opportunity for Tai Tokerau to have the deputy Prime Minister," he said.
Mr Harawira was quick to congratulate Mr Davis.
"There will be challenges for him to come. No doubt a number of them will be coming from me. But today's an important day for Kelvin and I wish him all the best," he said.
Mr Davis was elected to Parliament as a list MP after losing his Te Tai Tokerau bid to Mr Harawira in 2008. He failed again in the 2011 by-election, and lost his list seat in the 2011 general election, at which point he announced his retirement from politics.
He came back though, and won the electorate vote in 2014.