The WikiLeaks founder will pre-record an address to the Splendour forum audience as part of a panel session on Friday 29 July.
Assange will use his address to speak about the truth behind WikiLeaks and his arrest, festival organisers said.
Assange is under house arrest without charge in the United Kingdom, awaiting a court's decision on a bid by Swedish authorities to question him on allegations of sexual assault.
The Splendour panel, now in its second year, will be held at noon on the Friday with Assange's session called 'Big Brother v Little Brother: From government and big business to WikiLeaks and anonymous, who really controls our online secrets'.
The panel will be moderated by The Chaser's Julian Morrow and headlined by Assange's mother, Christine Assange.
"Splendour In The Grass is honoured to have both Julian Assange and his mother Christine Assange appear at Splendour Forum and we look forward to hearing their views on these important issues,'' Splendour In the Grass co-promoter Jessica Ducrou said.
This year's Splendour In The Grass festival features: Coldplay, Kanye West, Jane’s Addiction, The Hives, Pulp, The Living End, The Mars Volta, Regina Spektor, Bliss n Eso, Pnau, Mogwai, DJ Shadow, Friendly Fires, Glasvegas, The Grates, Devendra Banhart and The Grogs, Modest Mouse, The Middle East, Kaiser Chiefs, James Blake, Kele, The Vines, Elbow, Eskimo Joe, Noah and The Whale, Children Collide, Thievery Corporation, Cut Copy, Isobel Campbell and Mark Lanegan, Bluejuice, The Kills, Black Joe Lewis and The Honeybears, Architecture In Helsinki, Foster The People, The Panics, Jebediah, The Vaccines, Gomez, Boy and Bear, Gotye, Does It Offend You, Yeah?, Cloud Control, Mona, Sparkadia, Warpant, Muscles, Fitz and The Tantrums, The Jezabels, Drapht, British Sea Power, Tim & Jean, Leader Cheetah, Grouplove, Seeker Lover Keeper, Yelle, Kimbra, Phrase, Oh Mercy, Danananananykroyd, The Black Seeds, Marques Toliver, The Holidays, Ghoul, Liam Finn, The Herd, Young The Giant, Guineafowl, Hungry Kids of Hungary, Jinja Safari, Wild Beatss, Illy, Cut Off Your Hanes, Gareth Liddiard, Alpine, World’s End Press, Mosman Alder, Lanie Lan, The Aston Shuffle, Flight Facilities, D-Cup, Ajax, Hoodrat and Dangerous Dan, Light Year, Hoops, Cassian, Wax Motif, Kato, Toni Toni Lee, Charlie Chux, Tranter.
The three day festival will be held across Friday 29th to Sunday 31st July at Woodfordia, near Woodford, south-east Queensland.