TV Line says that the actor will appear in two episodes of the ABC drama.
His character is described as a "resourceful entrepreneur who strives to look as American as possible".
Marek will appear in the show alongside guest star Adrian Pasdar, who has signed up to play an FBI agent.
Marek previously played Oskar in Ugly Betty and has also appeared in shows including The Sopranos and Law & Order: Criminal Intent.
Castle airs on Mondays at 10/9c on ABC.