The Ukrainian president spoke via a video message played ahead of The Libertines’ stage-opening set on the big screens at the Other Stage on Friday.
“The festival resumes this year after a two-year break, the pandemic has put on hold lives of the millions of people around the world, but has not broken,” Mr Zelensky told the crowd of thousands.
“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.
“That is why I turn to you for support Glastonbury the greatest concentration of freedom these days and I ask you to share this feeling with everyone whose freedom is under attack.”
Mr Zelensky said Ukraine “will not let Russia’s war break us” and that he wants the war to stop before it “ruins people’s lives in other countries of Europe, Africa, Asia, Latin America”.
“Spread the truth about Russia’s war, help Ukrainians who are forced to flee their homes because of the war,” he said.
“Time is priceless and every day is measured in human lives. The more people join us in defending freedom and truth, the sooner Russia’s war against Ukraine will end. Prove that freedom always wins!”
He finished his message by saying “Slava Ukraini”, which translates as “glory to Ukraine” in English, which was met with loud and rolling cheers and applause across those gathered at the stage in Worthy Farm, Somerset.
Mr Zelensky also called on people to visit his United24 charity platform, which collects donations to aid Ukraine’s response to the Russian invasion.
At the same time, Ziggy Marley opened the Pyramid Stage with a set paying tribute to his father, the late reggae pioneer Bob Marley.
The singer and guitarist, 53, played a number of his father’s hits including I Shot The Sheriff, Jamming and Is This Love before closing with One Love.
Performing against a backdrop of photos of his father, who died in May 1981 aged 36 from skin cancer, Ziggy told the crowd: “It is good to be here. Today, my friends, I am here on behalf of my father.”
It comes before Billie Eilish will make history when she takes to the Pyramid Stage on Friday night as Glastonbury Festival’s youngest ever solo headliner.
The Grammy-winning singer, 20, will perform alongside her brother and co-writer, Finneas O’Connell.
The US pop star made her Glastonbury debut in 2019 when she performed on the Other Stage and treated crowds to a string of tracks such as Bad Guy and You Should See Me In A Crown.
The weather is set to be dry during her performance, despite the high chance of showers throughout the afternoon.
On the day Eilish headlines Glastonbury, Sir Paul McCartney will be warming up for his Saturday headline slot by performing at a Somerset music venue.
Apart from Eilish, the line-up for the Pyramid Stage on Friday includes Sam Fender, Robert Plant and Alison Krauss, Crowded House, Rufus Wainwright and Wolf Alice – whose appearance hangs in the balance because of travel problems.
Other acts performing on Friday include the Sugababes on the Avalon Stage, and Foals and St Vincent on the Other Stage, which also features Friday performances from Kae Tempest and The Libertines.
Eurovision winners Kalush Orchestra will also mark their first performance in the UK since their win, with a performance on Shangri-La’s Truth Stage on Friday’s bill.