The Scottish government said the developments - Neart Na Gaoithe, Inch Cape Offshore Limited, Seagreen Alpha and Seagreen Bravo - could generate up to 2.284 GW of electricity, and provide enough energy to power over 1.4 million homes.
Neart Na Gaoithe is set to see the delivery of up to 75 turbines, Inch Cape Offshore Limited aims to build up to 110 turbines, while Seagreen Alpha and Seagreen Bravo combined are planned to consist of up to 150 wind turbines.
The Scottish government said the consents were granted subject to "strict conditions" that it said would "mitigate and monitor a range of potential impacts including those in relation to birds and other environmental considerations".
Ewing said the wind farms could generate a combined gross value added of between £314 million and £1.2 billion in Scotland over their lifetime.
He added: "Granting consent for these developments will enable them to bid for an offshore wind contract for difference (CfD) under the UK Government’s Electricity Market Reform process.
"The budget for offshore wind (and other less established technologies) in the first of these rounds scheduled for autumn is £235 million, thought to be enough to support around 800 MW of offshore wind in UK waters."
But the approval has prompted a warning from the Royal Society for the Protection of Birds Scotland that the schemes could be among "the most deadly" in the world for seabirds.
RSPB Scotland said the consents would threaten colonies of gannet, kittiwake, puffin and razorbill that breed along the coast and forage for food in the surrounding seas.
Stuart Housden, director of RSPB Scotland, said: "RSPB Scotland wants to see the development of offshore wind in Scotland but it must not be at such massive cost to our internationally important seabirds.
"We will be considering carefully what further steps we can take in the coming days to ensure these decisions are fully compliant with the requirements of EU conservation directives."
The Neart Na Gaoithe can be found by clicking the link below
The Inch Cape can be found by clicking the link below
The Seagreen Alpha can be found by clicking the link below
The Seagreen Bravo can be found by clicking the link below