The East of England Co-operative Society is the largest independent retailer in East Anglia, comprising some 200 trading outlets across Essex, Sussex and Norfolk.
Kevin Warden, the group's local sourcing manager, said: "We're delighted to welcome Cornerways on board. Last summer we trialled their tomatoes in a smaller number of stores and they were a big success, so this year it's great to have them fully on board for the whole season.
"We had great feedback from our customers, who appreciated the tomatoes' great flavour, aroma and freshness - made possible by our pledge to get the product from field to store within 48 hours of picking."
Cornerways sales and planning manager Jonny Lambert added: "The business is dedicated to operating in a sustainable way and reducing its impact on the environment, so signing up to Sourced Locally is a great way to help achieve that.
"It's going to be great news for customers because we pick our tomatoes ripe and ready to eat, so they are extremely sweet and flavoursome when they hit the shelves. We'll be able to offer a wide range of local toms and we'll also try out some exciting new varieties over the season."
All of the tomatoes are packed on site in a modern packhouse, minimising handling and transport and allowing despatch to the East of England Co-op's distribution centre directly from the nursery for delivery to stores on the same day.
From now until mid November, Cornerways will supply almost 50 food stores with a range of local tomato varieties including baby plum, large vine, cherry, cocktail and salad tomatoes.