According to Deadline, the pair join Liam Neeson as stars in the upcoming thriller. Additional cast-mates include Diana Kruger, Jessica Lange, Adewale Akinnuoye-Agbaje, Danny Huston, Alan Cumming, Ian Hart and Colm Meaney.
The story follows private detective Philip Marlowe (Neeson), who is tasked with locating the former love of a wealthy heiress. Drawn into the underbelly of Hollywood, Marlowe stumbles into the crosshairs of an actress and her ambitious daughter.
Melchior and Arnaud are pegged to play siblings, Lynn and Nico Peterson. The significance of their characters is yet to be revealed.
Melchior drew attention earlier this year for her portrayal of Ratcatcher 2 in The Suicide Squad. She previously featured in The Black Book and provided the voice of Spider-Gwen in the Portuguese version of Spider-Man: Into the Spider-Verse.
Production on Marlowe is currently underway in Ireland and Spain.