Frederiksen, aged 41, will become the country's youngest ever prime minister after finalising a deal to form a minority leftist government.
“It is with great pleasure I can announce after three weeks of negotiations, we have a majority to form a new government,” she said.
“Now we have reached the goal… we have shown that when Danes vote as they have done, a new majority can turn their hopes into actions,” said Mette Frederiksen, who will become prime minister in a country where minority governments are the norm.
The opposition Social Democrats won a June 5th general election as expected, ousting Liberal prime minister Lars Løkke Rasmussen's minority government after several of his key allies suffered scathing losses at the polls.
Frederiksen said she will present the 18-page agreement on Wednesday, with the new government expected to be unveiled on Thursday.
The agreement was reached after 20 days of negotiations between Frederiksen's party and the three other parties in the ‘red bloc’ of traditional allies on the left of Danish politics: the Social Liberals (Radikale Venstre), Socialist People’s Party and Red Green Alliance.
The 20 days were the longest period taken to form government following an election since 1988.
“It is a political document, one of the first in the world that really defines green ambitions,” she said.
“We will develop a climate plan, a binding law on climate and reduce greenhouse emissions by 70 per cent.”