The cameras would cover all inshore areas where fishing posed significant risks to protected species, and record activity on vessels responsible for about 84 per cent of the inshore catch, by weight.
While the capital and operating costs were difficult to assess, they were estimated to be around $40m to $60m over four years.
That would include research into new camera technology and digital monitoring developments.
Nash said the roll-out of on-board cameras was another step to modernise the fishing industry, while providing the transparency demanded by domestic and international markets.
"The decision also supports the economic recovery for communities who depend on fishing for their livelihoods."
The roll-out comes after the Government last year funded cameras on 20 fishing vessels in areas that pose the highest risk to Māui dolphins, off the West Coast of the North Island.
Around 830 boats in the inshore fleet were also required to electronically report their catches and positions.
Seafood NZ's Jeremy Helson welcomed the announcement. He said his group looked forward to "continuing to work with government on some of the other issues holding up implementation".
Forest & Bird chief executive Kevin Hague also welcomed the move, which came after years of calls for action from conservation groups.
"Industry now needs to come to party and back the regulations and programme needed to make this happen," he said.
"Too often what happens at sea is out of sight and out of mind and there is a chronic, widespread problem of illegal misreporting that needs to end."
The group referred to data from the Government's own annual report on highly migratory fish fisheries, which revealed that fishers were nine times more likely to report bycatch if there was an observer on board.
Forest & Bird also gained data under the Official Information Act that showed that in the set net fishery penguin bycatch was almost exclusively reported on vessels that had observers.
"The public wants a fishing industry it can be proud of and cameras on boats is an important step towards achieving this," Hague said.
Greenpeace, however, argued that cameras should be rolled out across New Zealand's full commercial fishing fleet, which was made up of 1500 registered vessels.
"Without that, we are going to continue to see the same problems for the ocean, which is now seriously struggling," the group's oceans campaigner, Jessie Desmond, said.
"Time and again, this Government has pandered to commercial fishing rather than pushing ahead to get this long-overdue programme rolled out."
Global call for action on dolphins, whales
It comes as more than 250 experts from around the world have signed an open statement to global leaders calling for action to urgently address the precarious situation of many populations of whales, dolphins and porpoises.
This group of cetacean species face extinction a range of threats from harmful human activity such as incidental bycatch by fisheries, chemical and noise pollution, global warming and ship strikes.
The scientists say that of the 90 living cetacean species, more than half now have a concerning conservation status, and the trend of action coming "too little too late" must end.
Without urgent action, they predict the Northern Atlantic right whale could vanish, along with the critically endangered vaquita in Mexico which sits "poised on the knife-edge of extinction."
"New Zealand has a rich and diverse fauna of marine mammals with almost half the world's cetaceans alone having been reported in our waters," said Massey University marine biologist Associate Professor Karen Stockin, who served as the New Zealand contact on the letter.
"However, as part of the 2019 threat status of New Zealand marine mammals, we know some are doing better than others."
Currently, New Zealand has four nationally critically endangered species (Maui's dolphin, Bryde's whale, orca and Southern elephant seal), one nationally endangered species (bottlenose dolphin) and two nationally vulnerable species (Hector's dolphin, New Zealand sea lion) listed.
"While threats and extinction risks posed to New Zealand's endemic species such as Hector's and Maui dolphins rightly dominate our focus, in many cases, we remain unaware of the local extinction risks which silently emerge around us," Stockin said.
"For example, while not all may agree on the recently assigned higher New Zealand threat status of bottlenose dolphin over our endemic Hector's dolphins, this nonetheless demonstrates the point on how local extinction risks can emerge quickly and relatively unnoticed."
The statement reads: "The lack of concrete action to address threats adversely affecting cetaceans in our increasingly busy, polluted, over-exploited and human-dominated seas and major river systems, means that many [populations], one after another, will likely be declared extinct within our lifetimes ... Whales, dolphins and porpoises are seen and enjoyed all over the world, and are valued as sentient, intelligent, social and inspiring species; we should not deny future generations the opportunity to experience them. They are also sentinels of the health of our seas, oceans and, in some cases, major river systems and the role of cetaceans in maintaining productive aquatic ecosystems, which are key for our survival as well as theirs, is also becoming clearer."
