Approved by the Department of Energy and Climate Change (DECC), Npower Renewables' Gwynt y Mor Offshore Wind Farm, 16km from Llandudno, will comprise 250 turbines with a generating capacity of 750MW.
Its generating capacity as an offshore wind farm will be second only to the planned 1GW London Array scheme planned for the Kentish coast.
"The North Wales coast is set to become a powerhouse for renewable energy. Gwynt y Mor will be the largest of four offshore wind farms which combined will have the potential to power the equivalent of around 680,000 homes with green electricity," said Energy and Climate Change secretary Ed Miliband.
The other North Wales schemes are the 30 turbine North Hoyle and 25 turbines Burbo, both
operational, and the 25 turbine Rhyl Flats scheme, which is into the latter half of its construction phase.
"The UK is leading the world in offshore wind, and the developments
off the coast of North Wales will help keep us front runners," added Miliband.
A British Wind Energy Association spokesman said: "This is fantastic news. Gwynt y Mor is a landmark project both for Wales and the United Kingdom as a whole. It brings the total offshore
projects with planning approval to 4.5 GW, solidifying UK's position as leader in offshore wind energy. It will also set us well on our way towards reaching our 2020 renewable energy targets."