The windfarm will have the potential to supply power to 415,000 homes
The world's largest offshore windfarm is to be built off the Suffolk coast in a contract worth almost £2bn.
The Greater Gabbard scheme, to be sited 23km (12 miles) off the coast, will have the potential to supply power to 415,000 homes, the government said.
Power from the 140 turbines would help cut carbon dioxide emissions by 1.5m tonnes a year - equivalent to taking 350,000 cars off the road.
It is a joint venture between Airtricity and US firm Fluor.
Sub-contracts, which could benefit local companies, are expected to be announced soon.
The windfarm will be placed close to two shallow sandbanks - the Inner Gabbard and the Galloper.
It will occupy 150 sq km within the outer Thames Estuary strategic wind farm area.
The government granted approval for the Greater Gabbard scheme in February, last year.
The decision to grant consent was taken after a thorough consideration of the possible impacts of the project on a range of environmental and other issues, a ministerial statement said.
Airtricity is the renewable energy development division of Scottish and Southern Energy (SSE).
Ian Marchant, chief executive of SSE, said: "The UK wants to respond to climate change and become more self-sufficient in energy, so it makes sense to exploit the excellent resource that UK offshore wind represents."
Mr Marchant said that on completion Greater Gabbard will be the largest offshore wind farm in the world.