Trachtenberg, 27, of "Gossip Girl" fame plays Marina Oswald. Lee Harvey Oswald was accused of killing President Kennedy on Nov. 22, 1963, but his role in the assassination has been debated by conspiracy theorists.
"I am so excited for the challenge to portray Marina Oswald, and to do my first role speaking only in Russian," Trachtenberg said. "I'm the only actor playing someone who is still alive, so I want to stay as true to her as possible.
"This is a story about JFK's assassin, Lee Harvey Oswald, and his wife Marina. And it is fascinating."
"Killing Kennedy" is based on the book of the same name written by Bill O'Reilly and Martin Dugard. Trachtenberg plays alongside Will Rothhaar as Lee Harvey Oswald and Rob Lowe and Ginnifer Goodwin as John and Jacqueline Kennedy.
The project is currently in production in Richmond, Va., and is set to air on National Geographic Channel with the 50th anniversary of Kennedy's assassination.