A new deal was signed off today with renewables companies.
Areas off the north coast and South Down have been earmarked for development, the seabed's owners the Crown Estate said.
The projects could deliver 800 megawatts of electricity and power more than a fifth of homes, experts said. Development is expected to begin before the end of the decade.
Energy Minister Arlene Foster said: "Today's announcement by the Crown Estate represents a major milestone for Northern Ireland."
The Estate, which grants seabed lease development rights for offshore renewable projects, said agreements had been signed with First Flight Wind Ltd, Tidal Ventures and DP Marine Energy Ltd of Ireland, and DEME NV (Dredging, Environmental and Marine Engineering) of Belgium.
The companies secured leases for a stretch of seabed between Torr Head and Rathlin Island and another section off the coast of Ardglass, Co Down.
Two north Antrim sites would contain two tidal stream projects generating 100MW each. An offshore wind turbine project is planned for south-east Co Down creating 600MW of energy.
It is part of the Executive's plan to significantly reduce reliance on fossil fuels by 2020. The Executive requires 40 per cent of electricity to come from renewable sources by 2020.
Foster added: "The development of offshore renewables is an excellent opportunity for Northern Ireland in so many ways, energy security and diversity, climate change mitigation, a contribution to the Executive's 2020 (renewables) targets and the business supply chain opportunities for local companies over the next few years as these projects come on stream."
The consortium First Flight Wind, which includes one of northern Europe's leading energy companies (DONG Energy), has been selected to develop an offshore wind farm off the south-east coast of Co Down. It could deliver up to 600MW of generating capacity, supplying up to a fifth of Northern Ireland's 2020 electricity requirements.
The other two tidal stream projects will together deliver 200MW and the total new planned capacity announced today is equivalent to demand from between 200,000-300,000 homes.
Benj Sykes, director of First Flight Wind, said: "Northern Ireland stands out as having a real opportunity now to become a major contributor to the offshore wind market globally."
He added: "This is a new venture for Northern Ireland and for First Flight Wind and I am confident that we will secure benefits both in energy and in the wider sense for Northern Ireland for many years to come."
First Flight Wind will be unveiling its proposed community consultation programme in Newcastle, Co Down, on October 24 and will hold public information days in November. The consortium, which also includes B9 Energy Offshore Developments Ltd and RES Group, will meet interested parties and seek feedback on the community consultation programme proposed for the development stage of the project. The consortium will also be undertaking environmental impact assessments. Applications for consent are expected to be submitted to the authorities in 2015, with projects expected to start development from 2016/17 onwards.
Rob Hastings, director of energy and infrastructure at the Crown Estate, which owns the seabed in all UK waters, said there was still a long way to go as the companies take their proposals forward and carry out detailed surveys and planning work before their proposals are submitted for consent.
"We are very pleased to achieve this important milestone, and will continue to work closely with Northern Ireland Executive and developers to progress projects and attract investment, with the aim of helping meet Northern Ireland's targets on renewable energy production," he said.
Northern Ireland already has a tidal power installation at the Narrows in Strangford Lough.