The plant was created by introducing the genes from the snapdragon, a garden flower that allows them to produce a type of nutrient that prevents cancer.
When these tomatoes were fed to mice genetically engineered to have cancer the animals' lifespans were significantly extended.
The researchers hope that the "super-tomato" could help people meet the government's recommendation that everyone should eat five portions of fruit and vegetables a day.
"Most people do not eat five portions of fruits and vegetables a day, but they can get more benefit from those they do eat if common fruit and veg can be developed that are higher in bioactive compounds," Times Online quoted Professor Cathie Martin, of the John Innes Centre, Norwich, as saying.
The team believes that the new discovery will open up new pathways for the use of genetically modified (GM) foods.
The new tomatoes are coloured deep purple because, in the snapdragon, the function of the genes is to produce anthocyanins, the pigments that give the flowers their deep colours.
Anthocyanins are also believed to offer protection against cardio-vascular disease and age-related degenerative diseases. It also improves eyesight and hinders obesity and diabetes.
"This is one of the first examples of a GM organism with a trait that really offers a potential benefit for all consumers," said Martin, who now plans to test the tomatoes on humans.
Pete Riley, of GM Freeze, who is against the use of GM crops until more is known about them, said the idea of creating GM superfoods was fundamentally flawed.
"If you have an ordinary balanced diet there is no need for these weird new vegetables," he said.
"This is just the latest in a series of promised superfoods, none of which have yet made it to the supermarket. They are also very unlikely to benefit the world's poor who have the greatest need of better nutrition," he added.
The study appears in Nature Biotechnology.