However, Dexter suggested he already knows what the report will say.
"I think it's going to show what we've been saying all along: that this is the lowest-cost alternative," he said after a speech before the Halifax Chamber of Commerce.
"Those who are arguing against this are arguing in favour of higher rates."
At first, Dexter declined to say who was preparing the report or how long it has been in the works, indicating that he didn't want the media pestering the firm.
A few hours later, his press secretary issued a statement saying John Dalton, president of Power Advisory in Carlisle, Mass., has been preparing the $85,000 assessment since September.
Dexter said the report will be made public in January, before the province's Utility and Review Board starts public hearings on the so-called Maritime link — the subsea electrical cable that will connect Nova Scotia with the Newfoundland and Labrador power grid. The link is estimated to cost $1.3 billion to $1.5 billion.
That portion of the Muskrat Falls project is supposed to be built by a subsidiary of Emera Inc., parent of Nova Scotia Power Inc., the province's privately owned electric utility.
The company expects to sanction the link before it files an application with the Nova Scotia Utility and Review Board as the two processes are separate, a spokeswoman for Emera said.
The regulator filing is expected in mid-January, Sasha Irving added.
Last week, Prime Minister Stephen Harper signed off on a loan guarantee for the project.
On Wednesday, Dexter said an independent assessment of Muskrat Falls is needed because energy customers deserve to know more about the development, which is expected to cost up to $7.7 billion.
When asked why his government hadn't mentioned the assessment before, Dexter said: "I told you about it when it was appropriate to tell you."
Critics in Newfoundland and Labrador have long complained that the many assessments used to justify the project there have lacked independence. Dexter said he didn't accept that criticism.
"There's been lots of review of it and lots of independent numbers," he said.
Progressive Conservative Leader Jamie Baillie said Dexter has effectively dismissed the possibility that other sources of energy, including natural gas, wind energy and electricity from dams in Quebec, could be cheaper options for the province.
"What I heard the premier say today is that he wants an independent review, but we're going ahead anyway," Baillie said. "As premier, he's already declared the outcome. When you do that it's not independent."
Baillie said it made little sense for the premier to endorse the project before receiving the assessment.
"What people expect their premier to do is to stand up for them ... by not taking a position until all of the options have been explored," he said. "The fact that he signed on the dotted line first and is reviewing second means he has it backwards."
Later Wednesday, the Newfoundland and Labrador legislature passed a motion in support of Muskrat Falls.