The firm will purchase 50% of the electricity generated by the 48-turbine Fallago Rig wind farm, which is located north of Lauder in the Scottish Borders.
The agreement is said to be worth around £300m over the next two decades.
Brendan Dick, BT Scotland Director, said the deal "underpinned BT's long-term commitment to the digital fabric of Scotland over the next 20 years."
He added: "It's fantastic that all of our Scottish infrastructure and estate will be matched with energy from renewable sources in Scotland in a deal which gives us long-term price certainty.
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"BT is one of the UK's biggest consumers of electricity, and demand for our digital services, including fibre broadband, means we have to keep innovating to meet our needs in an environmentally responsible way.
"At BT we use the power of communications to make a better world. We're as committed to reducing our own carbon emissions as we are to providing products and services that help everyone live within the planet's resources."
He said the company reduced carbon emissions from its own operations by 25.5% globally during 2013/14.
"Our deal with Fallago Rig reinforces our commitment to make a positive contribution to society and the environment," he continued.
Welcoming the deal, Energy Minister Fergus Ewing said: "It is great news for Scotland and the environment that a company the size of BT is taking a local and sustainable approach to sourcing its electricity in Scotland from renewable and low carbon sources.
"With EDF Energy and BT now sharing 100%of the energy produced by Fallago Rig, it also secures generation at the site for the long-term future and shows the importance of Scottish renewable energy to Scottish-based businesses and their customers."
Fallago Rig is the fifth largest onshore wind farm in the UK, and is majority owned by funds managed by Hermes GPE Infrastructure.
(JP/IT)
