The comedian, actor and author is joining the 46th staging of the annual event - marketed as a "festival of arts, faith and justice...energised by a progressive Christian worldview".
The 43-year-old has expressed an interest in exploring spirituality in the past - studying Christianity and other world religions at the University of London's School of Oriental and African Studies.
Other speakers included in the first release of line-up information include members of the environmental group Extinction Rebellion, journalist Paul Mason and the Lutheran pastor Nadia Bolz-Weber.
OUR FIRST LINE-UP NEWS FOR #GB19 IS HERE! #WitAndWisdom @rustyrockets @frankturner @BFreeTheatre @lspraggan @MusicNegrito @BrassAgainst @Soakofficial @nakhaneofficial @GregoryAIsakov @Sarcasticluther @paulmasonnews @ExtinctionR @leunigcartoons— Greenbelt Festival (@greenbelt) March 26, 2019
A statement released by the organisers said: "In a burning world, we're still somewhere to believe in.
"And we're bringing our own brand of hopeful revolution to Boughton House this August for a festival that's inclusive, open-minded, participatory and generous in spirit.
"Celebrating artistry and nurturing activism, Greenbelt Festival is bringing wit and wisdom to thrill, inspire and provoke across 24 stages, galleries, installations and outdoor performances."
Musical guests at Greenbelt 2019 will include Frank Turner & The Sleeping Souls, Lucy Spraggan and Fantastic Negrito.
Michael Leunig @greenbelt 2019! Wow. In residence all weekend. That alone is worth the entrance fee. Thank you.— Peter Barrett (@PeterGBarrett) March 26, 2019
Other performers including the Belarus Free Theatre, filmmakers Silent Uproar Productions and comedians Thom Monckton and Circo Aereo.
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