The birdlife protection charity said the move was part of its continued commitment to green energy.
Its consumption, of around 3.5GWh a year, would result in around 1,500 tonnes of carbon dioxide emissions if generated from fossil fuels, the charity estimates.
Harry Huyton, RSPB head of energy policy, said: “Switching to a green energy company like Ecotricity is one of the most powerful and easy steps that individuals and businesses can take to speed the transition to a low carbon economy.”