As the Friday afternoon sun dipped towards the horizon, some students at the University of Chile played ping pong or football and couples lounged and kissed in the last warmth of the day. But others had more serious matters on their minds: the wildly popular student uprising that has transformed the nation's political agenda. And for many of the protesters involved and those who sympathise with its aims, the face of the uprising is Camila Vallejo.

In a basement auditorium a group of 60 student leaders planned the next steps in their burgeoning revolution for free university education, with Vallejo centre stage.

Vallejo sat behind her battered laptop, a small blue notebook on her desk and a rapt audience in front of her. When she speaks, her hands fly about, like birds snatching invisible prey. Her language is pointed and clear but, mixed with constant doses of humour and self-deprecation, she keeps her charges laughing.

As the second female president of Chile's leading student body, known as Fech (Federación de Estudiantes de la Universidad de Chile), Vallejo – who is also a member of the youth arm of the Communist party, the JJCC – has presided over the biggest citizen democracy movement since the days of opposition marches to General Augusto Pinochet a generation ago.

The government response has reminded many older Chileans of that same dark era. Three days ago, on Thursday, Chilean riot police ambushed Vallejo and a group of fellow student leaders just after a press conference in downtown Santiago. "They [police] targeted the leadership with violence," said Ariel Russell, a University of Chile student who witnessed the attack. "We had not even started the march and the police apparatus was upon us."

Vallejo, a 23-year-old geography student, was singing and marching with a handwritten sign when a squad of military vehicles closed in and attacked her with jets of tear gas. A pair of trucks mounted with water cannons unleashed a barrage of water fierce enough to break bones and scrape a person across the pavement. Vallejo was soaked, a cloud of tear gas was then blasted on to her body. With her skin wet, the chemical reaction was massive and incapacitating. Vallejo was paralysed. Her body went into an allergic reaction and welts from the gas erupted over it.

"At first, we resisted, but it was intolerable," she told the Observer. "You could not breathe, it was complicated, we had to run away from the carabineros [police] then another water cannon hit us in the face with a different chemical, this was much stronger … my whole body was burning, it was brutal."

Over the next four hours, journalists were beaten and 250 people arrested. Twenty-five police were injured as masked youths with paint bombs and handfuls of rocks counter-attacked. All Thursday afternoon, downtown Santiago was awash in running street fights between heavily armoured police units and hundreds of protesters decked in shorts and tennis shoes, with scarves to shield them from the gas.

As squads of police attacked students, pedestrians and even an ambulance, Vallejo huddled up in an office, receiving medical care and monitoring the situation through mobile phone reports from a team of scouts at the edges of what quickly became a riot.

The government blamed Vallejo for the chaos; after all, she had made the much publicised call, mobilising her followers to congregate at Plaza Italia, a public park and march along the Alameda, the capital's main thoroughfare, which sits less than two kilometres from the lightly guarded presidential palace. Vallejo was quick to retort that public gatherings need no authorisation and that the police had illegally attacked students standing in a park.

Vallejo, an eloquent and attractive young woman who exudes self-confidence and style, took the violence in her stride and focused on what she sees as the positive achievements thus far. "For years, Chilean youth have been consumed by a neo-liberal model that highlights personal achievement and consumerism; it is all about mine, mine, mine. There is not a lot of empathy for the other," said Vallejo in her office, decorated with a large photograph of Karl Marx.

"This movement has achieved just the opposite. The youth has taken control… and revived and dignified politics. This comes hand in hand with the questioning of worn-out political models – all they have done is govern for big business and powerful economic groups."

In just a matter of months, Vallejo has been catapulted from anonymous student body president to Latin American folk hero with more than 300,000 Twitter followers. Type her name into Google and there are more than 160,000 results just from the past 24 hours. Brazilian students now parade her as a VIP guest at their marches, the Chilean president invites her to negotiate a settlement and when she calls for a show of strength hundreds of thousands of students throughout Chile take to the streets. As an adept and wildly popular social media phenomenon, Vallejo has risen to become the most recognisable face of the student protesters.

Throughout the six-month revolt, Chilean students – in many cases led by 14- and 15-year-olds – have seized the streets of Santiago and major cities, provoking and challenging the status quo with their demand for a massive restructuring of the nation's for-profit higher education industry. In support of their demands for free university education, since May they have organised 37 marches, which have gathered upwards of 200,000 students at a time.

Police repression has been frequent. Vandals who often use the cover of student marches to attack banks, pharmacies and utility companies are met by an armed force of riot police who routinely attack pedestrians and tear gas crowds of innocent civilians.

What began as a quiet plea for improvements in public education has now erupted into a wholescale rejection of the Chilean political elite. More than 100 high schools nationwide have been seized by students and a dozen universities shut down by protests.

Classes for tens of thousands of students have been suspended since May, and the entire school year might have to be repeated. Polls show an estimated 70% of the Chilean public backs the students' demands and an equal percentage find the government's proposal insufficient, according to figures from Chile's leading newspaper, La Tercera.

Widely admired for her eloquent speeches on Chilean television, Vallejo has gathered a cult following around the world that ranges from German folk rock tributes to videos from Latin America's largest university, the Universidad Nacional Autónoma de Mexico (Unam). "This internationalisation of the movement has been very important to us," says Vallejo who receives a daily deluge of fan mail and invitations to speaking engagements and seminars. "Here in Chile we are constantly hearing the message that our goals are impossible and that we are unrealistic, but the rest of the world, especially the youth, are sending us so much support. We are at a crucial moment in this struggle and international support is key."

In stark contrast to the students' popularity, the once beloved coalition known as La Concertación, which organised the overthrow of Pinochet and then ruled Chile from 1990 to 2010, has fallen into political obsolescence. La Concertación is now polling at just 11% approval. Sebastian Piñera, Chile's president, a billionaire businessman, has just 22% public approval ratings, the lowest ever in Chilean history.

"For 20 years they [La Concertación] reinforced the Pinochet model, they institutionalised it, modernised it without any profound changes. Now that this model is in crisis, they can't be part of the discussion as they are effectively comp- licit," explained Santiago student Ariel Russell. "Camila has an ability to deliver a very wide populist message, not populist just in terms of communicating to the poor, but also to the middle class… The youth now have more credibility than the traditional politicians."

• This article was amended on 9/10/2011 to correct factual errors regarding the abbreviation of Federación de Estudiantes de la Universidad de Chile (Fech) and to correctly attribute Vallejo's membership of the JJCC, not the full Communist party

http://www.guardian.co.uk/world/2011/oct/08/camila-vallejo-latin-america-revolutionary/print