Harington has the title role in the drama, which involves a Hollywood star's career being destroyed when people start making assumptions about his correspondence with an 11-year-old actor. Chastain is set to play the editor of a gossip rag. Portman and Hoult's roles, meanwhile, have yet to be revealed.
Dolan immediately followed his festival hit Mommy (2014) with It's Only The End Of The World. That one stars Léa Seydoux (Blue Is The Warmest Colour), Marion Cotillard (Rust And Bone) and Vincent Cassel (Black Swan) and is currently in post-production for a release sometime this year.
We will next see Portman and Hoult, meanwhile, during the same weekend in the spring. Portman has the long delayed Western Jane Got A Gun, which arrives on 20 May, while Hoult will reprise his role as Beast in Bryan Singer's X-Men: Days Of Future Past (2014) follow-up X-Men: Apocalypse on 19 May.