The new law was announced by Michael Gove following the death of teenager Natasha Ednan-Laperouse.
Natasha, from Fulham, west London, suffered a severe allergic reaction after unknowingly eating sesame contained in an artichoke, olive and tapenade baguette she had bought from a Pret a Manger at Heathrow Airport.
The 15-year-old died of anaphylaxis after collapsing on board a flight to Nice on July 17, 2016.
Her parents have previously called for the so-called law to make all pre-packaged food clearly show allergens, which they have discussed with the Environment Secretary.
"Natasha's Law" will require all food businesses to include full ingredients labelling on pre-packaged food, the Department for Environment, Food and Rural Affairs announced.
The legislation, which will apply to England and Northern Ireland, is due to come into force by summer 2021.Under current rules, food prepared on the premises in which it is sold - such as a packaged sandwich or salad made by staff - is not required to display allergen information on the package.
The new legislation Welsh Government environment minister Lesley Griffiths told journalists on Tuesday that they too will introduce rules - although more likely via regulation than law.
Ms Griffiths said: "I've been working with Defra on that, and we will certainly be part of it.
"I think it's really important people understand what they are eating, but it's unfortunate it takes a tragedy to make this happen".
Asked if it would be law or regulation, she said: "I'm not quite sure. I think it's probably a statutory instrument [rather than legislation] but we will certainly be taking part in that as well".
Natasha's parents, Tanya and Nadim Ednan-Laperouse, said the introduction of the law would be a "fitting legacy" following their daughter's death.
They said: "We are absolutely delighted that the Secretary of State has announced the Government's decision to go ahead with full allergen and ingredient labelling.
"While Natasha's Law comes too late to save our beloved daughter, we believe that helping save other allergy sufferers and their families from the enduring agony that we will always bear is a fitting legacy for her life.ill tighten the rules by requiring foods that are pre-packed directly for sale to carry a full list of ingredients, Defra said.Although the new legislation is due to be introduced by the summer, businesses will be given a two-year implementation period to adapt to the change, the department said.
The Government launched a consultation into food labelling laws in January, with businesses and allergy suffers invited to have their say on four options put forward by the department.
Proposals included mandating full ingredient listing, allergen-only labelling, "ask the staff" labels on all products, or promoting "best practice around communicating allergen information to consumers".
More than 70% of individuals backed the option for full ingredients labelling, Defra said, and recent advice from The Food Standards Agency recommended full ingredients labelling.
Mr Gove called Natasha's parents an "inspiration" following the announcement of the law.
"Nadim and Tanya Ednan-Laperouse have been an inspiration in their drive to protect food allergy sufferers and deliver Natasha's Law," he said.
"These changes will make food labels clear and consistent and give the country's two million food allergy sufferers confidence in making safe food choices."
Heather Hancock, chairman of the Food Standards Agency, said the change will mean "better protection" for allergic consumers.
Allergy UK chief executive Carla Jones also welcomed the announcement, saying the national charity was "delighted" with the legislation.Indeed even if Wales or Scotland were to become Independent then I would see no problem in following such legislation when introduced in England, or Scotland or even the Republic of Ireland.
"This move towards full ingredient labelling for pre-packed direct-sale food will improve the lives of the allergic customer and it is warmly welcomed here at Allergy UK," she added.
Defra said food businesses across the country had already taken steps to improve food labelling and were urging outlets to do all they can ahead of the implementation date to help consumers make safe food choices.
Perhaps that is what Plaid Leader Adam Price had in mind After independence, Mr Price argued that a Britannic Confederation between Wales, Scotland and England would enable more equitable cooperation between the parliaments, governments and judicial systems of each nation.