Despite training as a nuclear physicist at an elite Mumbai research reactor and then gaining a PhD in quantum physics from a top overseas university, Shiva switched to environmental activism. "I went from nuclear science to quantum physics and then to being a natural philosopher," she says. "I would describe my vocation as a combination of natural philosopher - the old, old notion of trying to understand nature in all the complexity, which is the original form of science - and as a protector of the Earth." Shiva's attempts to protect the Earth have brought her into regular conflict with big corporations, especially those patenting genetically engineered seeds. Shiva, 57, says this "biopiracy" is an attempt to hijack the global food supply. She sued one of the seed firms, Monsanto, but also founded Navdanya, a national network of "seed savers" and organic farmers. It has helped set up 55 community seed banks to preserve traditional seeds and trained more than half a million farmers in sustainable agriculture. Those wanting to learn about organic farming can sign up at the Bija Vidyapeeth or School of the Seed. "For me seed saving became a way of defending freedom in the face of patents and trade rules which to me sounded like a totalitarian regime," Shiva says. "We can't have freedom if we don't have seed freedom."

Shiva chose to have lunch with the Herald at an organic cafe run by Navdanya inside a popular Delhi crafts market, with tasty dishes made from "forgotten" crops such amaranth, jhangora and ragi (the latter two are varieties of millet). Organic lychee cordial and marsala tea are served in clay cups. To promote biodiversity, Navdanya promotes little-known pulses and grains. Explaining the ''forgotten foods" program, she says: "So many foods have gone out of use and often they are very nutritious and good for conservation." Shiva's campaign to save seed varieties is one reason she will receive the Sydney Peace Prize on Thursday. The jury recognised her "courageous leadership of movements for social justice - the empowerment of women in developing countries, advocacy of the human rights of small farming communities and for her scientific analysis of environmental sustainability". Shiva grew up in Dehra Dun, a bustling town in the foothills of the central Himalayas. She says her parents were feminists, even though the word didn't exist at the time. "That was their thinking and practice and I think it seeped into us," she says. "My inspiration for life is our parents, so many of the values we have come from them … they told us that if you live by your conscience there is no reason to be afraid. That's how I have been able to take on the likes of Monsanto, never having an equation of fear.''

Shiva describes her parents as "anti-religious but deeply spiritual" and herself as a Hindu "without the distortions of the current times". Social activism runs in the Shiva family. Her sister, Mira, is a medical doctor and well-known health activist while her brother, retired as an air force pilot, does voluntary work for Navdanya. Her adult son, Kartikeya, is a photographer in Mumbai. The Shiva sisters have recently campaigned jointly on some issues including genetically modified food. "Even though we have walked very different paths - my sister in health and me in agriculture - we now work very closely together," Shiva says. Shiva's mother, Jagbir Kaur, was a committed Gandhian. She once visited the Mahatma when he was jailed in Pune and insisted that the family wear clothes made of locally spun cotton. Before her seventh birthday, Shiva asked for a nylon dress in a popular style. Her mother told her that purchasing a nylon garment would help "get the next Mercedes for a millionaire" but buying one made from locally spun cotton would "provide the next meal" in the house of a poor woman. "She asked me to make a choice - it was my first lesson in political economy."

Shiva also draws heavily on Gandhian philosophy to guide her work. She says he showed people have "the freedom to say no and the duty not to co-operate with unjust laws''. What Gandhi did with salt, "we do with seeds", says Shiva in a reference to the Mahatma's salt march of the 1930s that marked the beginning of the end of British rule in India. Shiva's work with the women of Chipko shaped her first book, Staying Alive, which was published in 1988 to international acclaim. It drew parallels between the oppression of rural women and environmental destruction in India and established Shiva's reputation as a leading ecofeminist thinker. She later co-authored a book, Ecofeminism, with sociologist Maria Mies. Shiva describes ecofeminism as a "philosophy of inclusion" and is critical of what she calls a "catch-up model" of feminism where women are in a battle to simply mimic men. "Combining nature's liberation and women's liberation shows a different path that is good for all beings on Earth," Shiva says. "Ecofeminism is about giving both nature and women their rightful place."

In 1993 Shiva received the Right Livelihood Award - also known as the Alternative Nobel Prize - for "placing women and ecology at the heart of modern development discourse". Shiva is also well-known for her criticism of the Green Revolution. Many in India argue the fertilisers, pesticides and genetic engineering that combined to create the Green Revolution rescued the country from regular famines and a reliance on food imports. The Prime Minister, Manmohan Singh, has even called for a second Green Revolution to ensure crop yields continue to rise. However, Shiva believes high-tech agriculture is only a short-term solution that will ultimately destroy farmers and the land. She warns of the growing threat of violent conflict over basic resources, especially water, due to the subcontinent's unsustainable farming practices. ''When you run out of water it's a recipe for killing," she says. "Water really makes people desperate." Another of Shiva's targets is globalisation. "We have seen what it's done. It's a process that has pushed about 10 million Indian farmers off the land and 200,000 of them off to another world through suicides … globalisation in effect means all seeds are owned by Monsanto, all our grains and our breads are owned by Cargill and all our media gets controlled by four of five big media chains.''

Shiva estimates about 40 per cent of the world's climate problem "is related to industrial, globalised agriculture", therefore, she argues, 40 per cent of the solution requires labour-intensive forms of ecologically sustainable farming. But she is surprisingly optimistic about the prospects for change. "There are huge reasons for hope," she says, citing a raft of successful protests, including one that recently stopped plans to privatise water in Delhi, as proof that non-violent resistance can work. ''But even more importantly, look at all the seeds that have been saved, the half a million farmers who have been trained in organic [methods], and the growth in alternative movements all saying we will not go down the industrial path." A life's passion Born in Dehra Dun, 1952.

Trained as a nuclear physicist, switched to quantum physics. Awarded PhD from University of Western Ontario. Dissertation entitled, Hidden variables and locality in quantum theory. Founded the Research Foundation for Science, Technology and Ecology. Wrote The Violence of Green Revolution; Biopiracy: the; Water, Wars:; and the ecofeminist classic Staying Alive. Plunder of Nature and Knowledge

Privatization, Pollution and Profit Vandana Shiva will deliver the University of Sydney Peace Prize lecture, Making Peace with the Earth, at the Opera House on Wednesday.