About 450 new jobs will be created when two large stores open later this year.
Supermarket giant Asda has won its appeal to build a store in Rawreth Lane, Rayleigh, which bosses have said will create around 250 new jobs.
There will be another 200 new jobs in Southend when a huge B&Q store opens in Fossetts Farm in August.
Asda has won a long-running battle to build a medium-size store on the former Park School site, alongside a separate building with five shops, a cafe and space for a community hall, nursery and a health centre.
However, traders in Rayleigh fear the decision could have a serious impact on the town centre.
Edward Byford, who runs a butchers in the High Street, said: "I'm very disappointed that it has been approved.
"I think it will definitely take business away from the town centre. It won't kill off the shopping altogether, but traders will have to adapt."
More than 100 houses and flats have already been built on the former Park School site, as well as a leisure centre and a new primary school.
Residents have also battled against the store landing on their doorstep.
Steve Springham, of Rawreth Lane, said nearby residents were "bitterly disappointed" with the news.
He said: "This will have an impact on retail outlets in Rayleigh and Hullbridge.
"An Asda supermarket will bring a lot of traffic to the area to provide them with their anticipated £22 million turnover."
It has not been confirmed when the new shop will open.
Meanwhile, the new B&Q building is fast taking shape and should be completed by May, with an opening date in August.
The existing B&Q in Short Street, Southend, will be closed and the 60 jobs transferred to the new shop.
Alex McHaines spokeswoman from B&Q said: "There will be around 250 jobs in the new shop in total, which will include a range of jobs including shop floor and management positions.
"It is an exciting time for us, but it is still a little way off."
David Garston from Southend Council said he was delighted with the new jobs, which would benefit the whole area.
He said: "Traditionally there has always been a shortage of unskilled work in the Southend area, so this is excellent news.
"As part of our targets in connection with the Thames Gateway, the borough has to create 11,000 new jobs by 2021 and build 6,500 new homes."
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