Segel will replace Nicholas Hoult, who recently dropped out due to scheduling conflicts.
The movie, written by McDowell and Justin Lader, begins production in Rhode Island later this month.
The sci-fi love story is set in a world where the existence of an afterlife has been scientifically proven. Millions of people are now taking their own lives in the hopes that committing suicide is akin to pushing a reset button.
Redford plays the man responsible for the discovery, Segel portrays his son and Mara is the woman Segel’s character falls in love with who’s haunted by a tragic past.
“The Discovery” will be produced by Alex Orlovsky of Verisimilitude and James D. Stern of Endgame Entertainment, and financed by Endgame Entertainment and Protagonist Pictures. Julie Goldstein and Lucas Smith will oversee the project for Endgame, while Mike Goodridge, Dimitra Tsingou and Eddie Vaisman oversee it for Protagonist.
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McDowell recently made his feature film directorial debut on “The One I Love,” starring Mark Duplass and Elisabeth Moss.
ICM Partners and WME Global packaged the project and are representing domestic rights for the film. Protagonist is handling international rights.
ICM Partners represents McDowell and Lader. McDowell is also repped by Kenny Goodman at MGMT Management. Redford and Mara are repped by WME. Segel is repped by WME and Stacy Abrams of Abrams Entertainment.