Dunderdale said the federal government would cover $280 million of the investment for research and marketing, while the province will kick in the rest.
The deal follows concessions the premier has made toward reaching Canada's Comprehensive Economic and Trade Agreement with the European Union.
The pact is not expected to take effect for two years but would open up lucrative European seafood markets for the province's troubled fishery.
Dunderdale called the $400-million fund a historic injection that would be spread over three years starting in 2015 if CETA is finalized and signed as expected.
Dunderdale said she fought hard to speed up tariff-free EU access and is not concerned that exempting minimum processing rules, which require fish that is landed in Newfoundland and Labrador be processed in the province, will jeopardize plant workers or small industry players.
"We have levered everything we could possibly bring to the table to maximize benefits for the people of the province and we've done that, I think, in spades," she said.
"We don't see that there will be any impact as far as MPRs (minimum processing rules) are concerned. If somewhere along the line there is an impact ... there is a capacity to address it within this fund."
Dunderdale said her Progressive Conservative government will work with industry players to prioritize how the money will best be spent to brand and position provincial seafood in European markets.
The provincial fishery is a shadow of what it was before the 1992 commercial cod moratorium. But it's still a $1-billion industry that employs 19,000 people, many in rural regions.
Earle McCurdy, president of the Fish, Food and Allied Workers union, said the fund will help the fishery and plant workers take full advantage of the trade deal.
"I think it's a very good day, especially for coastal Newfoundlanders and Labradorians," he said.
McCurdy said he hopes a level playing field in Europe will mean new opportunities for about 90 processing operations in the province.
"Tariff-free access to European markets was a game-changing development for the industry," added Derek Butler, executive director of the Association of Seafood Producers.
CETA will give the province unfettered access to the world's most discerning seafood market, he said.
Conspicuously absent from Tuesday's funding announcement, which included much of the Tory government's 35-member caucus, was any representative of the federal government.
But Rudy Husny, a spokesman for International Trade Minister Ed Fast, said in an emailed statement that the trade deal will be of huge benefit to the province and the fund will help offset any downside to the agreement.
"The program will address fish and seafood industry development and renewal as well as workers whose jobs are displaced in future as a result of (minimum processing rules) no longer being applied to product destined for the EU."
Provincial Liberal fisheries critic Jim Bennett said offering to give up those protections in exchange for $280 million in federal cash is a reckless giveaway.
"We're getting $560 for every man, woman and child in this province for the Europeans to have unfettered access to our seafood for all time.
"This is a bad, bad day for us."
Bennett said small fish processors will be squeezed out of business with more local job losses to follow in outport communities. He said it's foolhardy for Dunderdale and the FFAW union to think local plants will be able to compete with processing wages in parts of Europe such as Spain and Greece, where unemployment tops 20 per cent.
"Plant workers are really done in this province," Bennett said. "The small ones will go first. This is like resettlement by sellout."