The move could also put pressure on other major UK retailers to follow suit, and affect how food in the future is sourced.
The company says that a total of 38 product lines will be switched, and that the value of all Fairtrade instant and ground coffee sold in UK supermarkets is likely to increase by 18 per cent, and the value of Fairtrade tea by approximately 30 per cent as a result.
Fairtrade coffee is on sale in all M&S stores from this week, while Fairtrade tea will be available from April.
"Our customers have told us they care about how our products are made and we want to help them make Fairtrade part of their retail habit," said Stuart Rose, M&S chief executive.
"I'm therefore delighted we are moving our entire range of tea and coffee to Fairtrade, which as a 100 per cent own brand retailer we are in a unique position to do. Our conversion will significantly increase the value of Fairtrade coffee and tea in the UK."
A recent YouGov survey commissioned by Marks & Spencer found that consumers are becoming more ethically minded with 78 per cent saying they would like to know more about the way goods are made including the conditions in the factories where they come from.
Some 59 per cent said they already purchase Fairtrade products and 18 per cent said they would buy Fairtrade items if they were more widely available on the high street.
Indeed, ethical considerations are increasingly dictating food purchases. Ruth Rosselson, a writer for the UK Ethical Consumer Research Association (ECRA), told FoodNavigator recently that factors such how companies sources their products, the impact they have on the environment and how they treat their workers are directly impacting how they spend their money.
"This ethical market is definitely growing," she said. "People are increasing asking where their products were made and how far they have come."
Issues such as sustainable sourcing and fair trade are therefore of increasing importance to both consumers and food makers.
"With this groundbreaking switch to Fairtrade, Marks & Spencer has gone further on tea and coffee than any other retailer to date," said Harriet Lamb, executive director of the Fairtrade Foundation. "It establishes Fairtrade firmly into its rightful place as part of normal, everyday life."
Marks & Spencer already sells Fairtrade-only tea and coffee in its 200 Caf Revive coffee shops, one of the largest chains in the UK, resulting in 35m cups of Fairtrade coffee being sold since September 2004.
This week's announcement coincides with the second phase of Marks & Spencer's 'Look behind the label' campaign designed to tell customers about the way products are sourced and made.
The Fairtrade Foundation certifies products with the Fairtrade Mark and promotes Fairtrade. Inspection and audit ensures the producers meet the Fairtrade standards of a democratic and participative structure where Fairtrade premiums are used to improve social conditions or the economic infrastructure.
Fairtrade Fortnight runs from 6 to 19 March 2006.