The 19-year-old activist led chants of “climate … justice” after delivering a rousing speech from the Pyramid stage which painted an apocalyptic picture of the future of the planet.
To cheers from thousands of festival-goers, Thunberg said: “We are approaching the precipice and I would strongly suggest that all of those who have not yet been greenwashed out of our senses to stand our ground.
“Do you not let them drag us another inch closer to the edge. Right now is where we stand our ground.”
Thunberg was introduced on stage by the Glastonbury co-organiser Emily Eavis, who described the Swedish teenager as “the most inspiring speaker of this generation”.
Drawing cheers of approval, Thunberg blamed world leaders for failing to halt the climate emergency and for creating “loopholes” that allow ecological destruction to go unchecked.
“It has not only become acceptable for leaders to lie – it’s almost what we expect them to do,” she said to applause.
She said it was time for society to start “creating hope” rather than waiting for it to arrive: “Hope is not something that is given to you. It is something you have to earn, to create. It cannot be gained passively from standing by passively and waiting for someone else to do something.
“It is taking action. It is stepping outside your comfort zone. And if a bunch of school kids were able to get millions of people on the streets and start changing their lives, just imagine what we could all do together if we try.”
Thunberg’s surprise in-person speech was announced on Saturday morning. She appeared shortly before a set by the American pop band Haim and just a few hours before Paul McCartney’s headline slot.
Under blazing sun on the fourth day of Glastonbury, Thunberg urged festivalgoers to “do the seemingly impossible” by helping to halt global warming before it is too late.
She added: “These crises are the biggest story in the world. And it must be spoken as far and as wide as possible, as far as our voices can carry and even further still.
“It must be told in the articles, newspapers, movies and songs; at breakfast tables, lunch meetings, family gatherings; in lifts and bus stops; and in rural shops … and music festivals like Glastonbury.”
Thunberg’s is the second high-profile speech of the festival after the Ukrainian president, Volodymyr Zelenskiy, delivered a video address to thousands of bleary-eyed revellers on Friday morning.
Zelenskiy described Glastonbury as the “greatest concentration of freedom” in the world as he urged campers to put pressure on politicians to end the war in Ukraine.
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To cheers from the crowd, he said: “We in Ukraine would also like to live the life as we used to and enjoy freedom and this wonderful summer. But we cannot do that because the most terrible has happened – Russia has stolen our peace.”
Founded in 1970 as a way to build support for the Campaign for Nuclear Disarmament, Glastonbury has retained its strong political bent over the last half-century even as the festival has widened out to a much broader audience.