Pret A Manger will list all ingredients including allergens on its freshly made products following the death of 15-year-old Natasha Ednan-Laperouse who had an allergic reaction after eating a Pret sandwich.
The teenager collapsed on a British Airways flight shortly after eating a baguette purchased at the chain. She had suffered an allergic reaction to sesame baked into the baguette.
The presence of the sesame was not highlighted on the packaging or on the fridge of the Heathrow Airport outlet in 2016, an inquest into her death heard last month. The coroner found that Ednan-Laperous had been "reassured" by the lack of specific allergen information on the packaging.
The announcement comes after Prime Minister Theresa May called for a review of food labelling laws on Tuesday.
Clive Schlee, chief executive of Pret A Manger, commented: "I said we would learn from this tragedy and ensure meaningful changes happen.
"I hope these measures set us on course to drive change in the industry so people with allergies are as protected and informed as possible. Nothing is more important to Pret right now."
But Beatrice, whose identity the BBC agreed to not disclose, told the broadcaster that she suffered an allergic reaction to sesame seeds in a Pret sandwich that landed her in hospital for 12 hours. She was told Pret had promised to start a full labelling trial at the start of this year.
"It's good that Pret has finally taken this action but the cost to the family is too high," she said. "It should never have happened. Why has it taken so long for them to introduce full labelling?"
Theresa May said the government would look at the food labelling responsibilities of individual companies. Her comments came after Environment Secretary Michael Gove told civil servants on Monday to investigate changing the law.