India's answer to Speakers' Corner attracts a motley crowd of activists. Men in white Nehru caps call for an expansion of India's creaking rail network and banks of TV cameras cover the latest political soap opera. Today, a disgruntled leader is on hunger strike against his own party. The noise of speakers shouting into sound systems wired up to car batteries is immense.

Kavita Krishnan, 41, a member of India's leftwing CPI-ML party, is here to campaign for the land rights of more than 700 million rural Indians. Since the gang rape of a Delhi student in 2012, she has emerged as a vocal champion of women's rights. Short, unassuming, but quietly formidable, Krishnan's willingness to defend rape victims, in a country where it's still the woman who loses her "honour" in a sexual assault, has made her a heroine to some, a "slut" to others.

"Women have every right to be adventurous," she told her fellow gang rape protesters in December 2012, dripping wet after being doused by water cannon. "We will be reckless, we will be rash. Don't tell us how to dress. Don't tell us when and where to go out. If girls want to go out at night to buy a cigarette is that a crime?"

That speech, posted online, went viral. "These issues were considered 'radical' before," she told the New Review. "After the gang rape, the support was huge. The media began to make space to discuss these issues."

India was rated the worst country for women among the G20 group of economies even before the Delhi gang rape took place. The survey, in June 2012 by TrustLaw, a legal news service of the Thompson Reuters Foundation, found that the combination of infanticide, child marriage and slavery accounted for India's dismal ranking. Despite the success of a handful of prominent female politicians, Krishnan finds India's political system undemocratic and misogynist.

"Politics is a very masculine space here," she says. "Women are subjected to enormous hate speech. Of course there's always vitriol in politics, but this is designed to intimidate women. One minister accused me of being a naxalite (armed revolutionary) and said I stood for 'free sex'. That's like shouting 'slut, slut' in public."

India's national politics are dominated by the Congress party of Indira Gandhi and by the Hindu-nationalist BJP. Krishnan's party, the CPI-ML, sits on the very fringes of power. It's only had two members elected to the national parliament. Its gender policies – opposing all violence and harassment of women, supporting equal rights to property, wages and freedoms – would be considered mainstream in most countries. But the CPI-ML also opposes nearly all foreign investment in India because, in its view, free-market policies place a greater burden on the poor.

"The BJP and Congress exist to maintain the status quo," says Krishnan. "It's easy not to address the questions of democracy, but I like that challenge."

Whether in politics or in her personal life, Krishnan has always seen herself as swimming against the tide. Her father, an engineer, read her Indian feminist poetry as a child, while her mother, a teacher, was often criticised by friends and family for the liberal way in which she raised her two daughters. At university, Krishnan shunned politics until a rightwing Hindu candidate held a rally on campus. She and her friends went along, insolently smoking to annoy him.

"We asked him what he would do if he was elected, and he said, 'There are lots of jails for women like you,'" she recounts, laughing. "I immediately went and signed up for the other party."