The decision follows a public inquiry last month following refusal of planning permission by Wellingborough and Bedford Borough Councils and Milton Keynes Council.
Inspector Trevor Cookson found that the scheme would cause limited harm to the landscape landscape and visual amenity. In his view, this was outweighed by the "urgent need for renewable energy as promoted in national and regional policies and the wider environmental and economic benefits that it would bring".
RWE npower renewables regional manager for eastern England Matt Pinfield said: "It is a superb location for a wind farm. It is well designed and appropriately sited and will generate enough energy to meet the annual average needs of thousands of homes each year. The Nun Wood Wind Farm will make a substantial contribution to clean energy supply and the reduction in emissions of greenhouse gases."
A spokesman for Bozeat Lavendon Oppose Turbines, a local group that has been contesting the scheme over the past six years, said: "We are still studying the inspector’s report to try and understand the clauses and caveats, but this really does look like it's over and we have lost our fight."