Her campaign - Women Say No to GMOs - will start with the launch of a petition on the internet.. It aims to persuade 50,000 women to sign up by Christmas to a "consumer's charter" demanding "the right of all consumers and farmers to choose to remain GMO free".
Ms Ruddock, with her partners, the food writer Lynda Brown and the Soil Association, has already signed women such as Anita Roddick, Jancis Robinson and Caroline Conran. But she is giving pride of place to a man: Paul McCartney.
An exception is being made for the former Beatle - the only man invited to get involved - on the grounds, said Ms Ruddock, that he will be representing "the McCartney family", especially his late wife Linda, a champion of vegetarianism and organic produce.
"I wouldn't prohibit men signing up," she said. "But the campaign is directed at women because we want the Government to be made aware of women's concerns."
The former chairwoman of the Campaign for Nuclear Disarmament (CND) - who was (unpaid) Minister for Women during Labour's first year in power - says it is women who have pushed GM food into retreat in Britain.
"The debate in the media has been discussed by men in grey suits and white coats," she said, "while those who are concerned with the effects have been labelled as hysterical and ill-informed."
But supermarkets have been forced to go GM-free because of consumer power, which has, she pointed out, been exercised mainly by women "who just refuse to buy the stuff".
She said that she has always been a campaigner, even during her 12 years in parliament, but today's launch brings her back to her roots. The daughter of market gardeners who studied botany at Imperial College, London, she took her first job with the campaigning group Shelter.
She joined CND when standing as a Labour candidate for Newbury in the 1979 general election. She said that "what really changed my life" was the decision, the next year, to site cruise missiles at the nearby Greenham Common.
She spent an enormous amount of time with the women protesting at the base and took over the chair of CND in 1981. After becoming an MP in 1987 she was quickly appointed to a front bench position, eventually becoming Shadow Minister for Environmental Protection. She seemed set for high office, but then it all fell apart.
She was replaced as Shadow Minister by Michael Meacher in the run-up to the last election and was deeply disappointed not to be made a minister immediately afterwards. She was finally, belatedly, given a job as Minister for Women, but without a ministerial salary. Although she believes she did "a very very good job" in the post laying the ground for major reforms, her job was scrapped after a year.
"You ask yourself what did I do wrong? Why did I fail? You ask everyone around you. Nobody told me anything. Nobody came up with a reason so I have to accept that it's one of the things that happen in politics." She said she wondered why she had put so much effort into politics when the fulfilment of office "was lost to me", and admitted she found it "very very hard to find a parliamentary role afterwards".
She found it "really hard to feel focused" after the front bench work was taken away. But she became interested in genetically modified food and last February was one of the first Labour MPs to break ranks with the Government's pro-GM policy - in an article in the Independent on Sunday. The campaign offers the chance to bring together two of her main concerns: women and the environment.
She does not expect to be offered a ministerial job again but is looking forward to the new start.
"Much as I wanted to be Minister for the Environment, much as I wanted to remain Minister for Women, I now begin to feel that there are some compensations in not being an office holder," she said.