The blockbuster deal - which is effectively a takeover bid with Sainsbury's acquiring a 58-percent stake in the combined group and Walmart the remainder - comes as long-established United Kingdom supermarkets battle fierce competition from German-owned discounters Aldi and Lidl and online U.S. titan Amazon.
"Both Sainsbury's and Asda have significant stakes in the clothing market, with forecast share for 2018 at 2.1% and 3.5% respectively".
Shadow business secretary has warned Rebecca Long-Bailey said a "duopoly" of the big supermarkets would emerge, which she said could be at the expense of manufacturers, suppliers and farmers while both Leeds West MP Rachael Reeves and Leeds Central MP Hilary Benn demanded assurances from Government that Asda's Leeds headquarters and its around 2,000 staff would be protected.
Tesco shares retreated by 0.9 percent while there were gaines for Morrisons (1.3 percent), Marks & Spencer (0.4 percent) and online rival Ocado (1.9 percent).
The cash and shares deal could also provide a potential exit route for Walmart, as Asda, which it bought in 1999 for £6.7 billion, has been struggling to grow over the last five years, with discounters Aldi and Lidl attracting its price-conscious customers.
Sainsbury's, formerly the second biggest supermarket, and Walmart-owned Asda, which held the third spot, said they plan to combine to overtake Tesco.
The transaction values Asda at £7.3 billion.
Sainsbury's is valued at around £5.9 billion.
Sainsbury's chairman, CEO and chief financial officer will run the company.
E. coli outbreak affecting more people, states
If you already have store bought romaine lettuce in your fridge, the CDC said you're better off not eating and throwing it away. Erring on the side of caution, Wise said: "People should not be eating any type of romaine lettuce".
"It was an unfortunate choice of song, from the musical 42nd Street which I saw previous year and I apologise if I have offended anyone", Mr Coupe said.
He said: "I stand by our statement".
Walmart will be a long-term shareholder and partner and will leverage its global scale and investment to support the combined business.
"We believe the combination offers a unique and exciting opportunity that benefits customers and colleagues", noted Walmart President and CEO Doug McMillon.
"We look forward to working closely with Sainsbury's to deliver the benefits of the combination".
Sainsbury's said the combination would generate synergies of at least £500 million and enable prices to be lowered by about 10 per cent on many products.
After the merger, the group will have a joint 2,800 stores, £51bn combined revenues and a 59% share of the total United Kingdom retail market - with Tesco's 27.6% and Morrison's 10.4% market shares, the top three supermarket groups (no longer four) would account for almost 70% of the total market.
Latest figures show that Tesco has a 27.6% market share, while Sainsbury's has 15.8% and Asda has 15.6%.
Sainsbury's was launched by a young couple, John James Sainsbury and Mary Ann Staples, when they opened a small London dairy shop on the day they married in 1869, according to the company's website.