The move would more than double the market for Fairtrade roast and ground coffee in the UK from 2,248 tonnes to 4,600 tonnes every year, the retailer said.
"This is a significant move for us because of the scale of tea and coffee we sell," said Sainsbury's chief executive Justin King. "This means a much larger number of producers in developing countries will benefit from the Fairtrade mark.
"After decades of selling huge quantities of tea and coffee, moving to 100% Fairtrade is an important milestone for our organisation, as well as Fairtrade producers."
Sainsbury's 45-strong coffee range is being re-launched in new packaging to mark the transition.
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