Introduced by festival organiser, Emily Eavis, the climate activist used her moment on the main stage to tell festival goers about what she says is "the biggest story in the world" - the truth about climate change.
The 19-year-old Swedish activist surprised crowds waiting to see American pop rock stars Haim at the Pyramid Stage on Saturday (25 June).
She appeared in front of the main stage, which can boast audiences of up to 100,000 people.
In her address to the festival she criticised world leaders for 'creating loopholes' for businesses that directly impact climate change and those who 'believe their money can buy them out of mass extinctions'.
The activist said: "The current climate crisis not the new normal... it will continue to get worse until we prioritise people and planet over profit and greed."
Talking to the massive crowd, the 19-year-old said places like music festivals, as well as schools, bus stops and rural shops - need to be places where information about the climate crisis is shared.
Speaking from the Pyramid Stage, she continued: “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."
"No one else is going to do this for us, it's up to us, you and me," Ms Thunberg's speech finished, before she encouraged the crowd to join in a 'climate justice' chant.
Set against a stage backdrop of the climate 'warming stripes', her message reflected the ambitions of her latest book.
Entitled 'The Climate Book', it examines the state of the planet and hopes to be "an essential tool for everyone who wants to help save it".
Thunberg brought together over 100 climate scientists, communicators and activists to show how the climate, ecological and sustainability crises connect across the globe.
The book will be published on 27 October.
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