The plan to bring power from the lower Churchill River in Labrador to Newfoundland then Nova Scotia using subsea cables was announced in November 2010 — just before he quit politics.
"From my own personal legacy perspective, I stand by this wholeheartedly," he said Wednesday outside the legislature.
"I've said from Day 1, I'd put my own money into this project if I could because I think it's just a great investment for the people."
Williams was unfazed by about 35 protesters who had gathered earlier outside. They're concerned that Muskrat Falls will cripple the province of just over 500,000 people with massive debt if it soars over budget.
"I can honestly say that this has been studied to death," he said.
Premier Kathy Dunderdale moved a private member's motion that the house of assembly support the development, which is estimated to cost between $7.5 billion and $7.7 billion. Debate was limited to a couple of hours on the biggest public expenditure in provincial history before the majority Tory government easily passed it over opposition objections.
"It is the best answer to our question: what is the least-cost option to providing needed power?" Dunderdale said as government members thumped their desks in approval.
"It will bring lasting benefits to the people of Newfoundland and Labrador."
Skeptics point out that the project has not cleared a single independent, regulated review.
Dunderdale said Muskrat Falls has been endorsed by global energy consultants, though they were hired and paid by her government. She has refused further review by the provincial Public Utilities Board since it declined last spring to endorse Muskrat Falls, saying it lacked updated information.
Now that Ottawa has offered a federal loan guarantee that would cut borrowing costs by about $1 billion, the province's Crown corporation Nalcor Energy and Nova Scotia private utility Emera (TSX:EMA) are expected to sanction the project in coming weeks.
Williams laughed when asked if he thought Prime Minister Stephen Harper, whom he openly battled over offshore royalties and equalization payments, would have given him a loan guarantee.
"Probably not," he said. "Maybe it's a good thing that I had moved on."
Dunderdale has said her province is expected to sanction Muskrat Falls before Christmas. A spokeswoman for Nova Scotia private utility company Emera said it is expected to do the same before mid-January.
Dunderdale refused to say when repeatedly asked Wednesday whether the development is viable with or without a federal loan guarantee.
"It's not going to fall apart," she said of the federal backing that relies on Emera's continued support.
"We've been through a set of negotiations that has been long and arduous. Emera's been at the table, we've been at the table with the federal government. We made sure that we protected the interests of the people of this province.
"So I'm telling you that if we sanction this project, that the loan guarantee will be available to the people of the province."
Liberal Opposition Leader Dwight Ball called the government's approach on Muskrat Falls "an insult to democracy."
"I say shame on you, premier," he said during the daily question period that preceded the two-hour debate.
NDP Leader Lorraine Michael asked of Dunderdale: "How can she sanction a project that lays all this considerable risk squarely on the backs of the ratepayers of this province?"
During the earlier protest outside, skeptics said they fear Muskrat Falls will spell disaster for a once have-not province that has only recently enjoyed the wealth of offshore oil royalties.
"I'm disappointed," said protester Con O'Brien.
"We're playing a game of Russian roulette with our money. We're 515,000 people. We can't afford to pay it.
"God help us."