FX's X-Men take Legion is adding to its cast.

Newcomer Jeremie Harris has booked a series-regular role on the drama pilot from Fargo's Noah Hawley, The Hollywood Reporter has learned.

The Legion pilot introduces the story of David Haller (Downton Abbey's Dan Stevens), a man who may be more than human and who has struggled with mental illness since his teenage years. Diagnosed as schizophrenic, David has been in and out of psychiatric hospitals for years. But after a strange encounter with a fellow patient, he is confronted with the possibility that the voices he hears and the visions he sees might be real. In the comics, David is the son of X-Men founder Charles Xavier (aka Professor X) and Israeli Holocaust survivor Gabrielle Haller. The character first appeared in New Mutants No. 25 in March 1985.

Harris will take on the role of Ptonomy, an outsider by nature, stand-offish and sardonic, who is a former child prodigy who feels trapped in the past.

Harris, a Juilliard graduate, is currently recurring on Netflix's Baz Luhrmann's 1970s hip-hop drama The Get Down. His credits include playing Langston Hughes in HBO's Bessie as well as episodes of CBS' Blue Bloods and Person of Interest. He's repped by UTA.

Harris joins a cast that also includes Parks and Recreation's Aubrey Plaza as well as Fargo's Jean Smart and Rachel Keller.

Legion hails from FX Productions and Marvel Television, with FXP overseeing production. Hawley, who has an overall deal with FXP, will write the pilot and serve as an executive producer alongside Lauren Shuler Donner (X-Men: Days of Future Past, Wolverine), Bryan Singer (X-Men: Days of Future Past, Superman Returns), Simon Kinberg (X-Men: Days of Future Past, The Martian) and Marvel's Jeph Loeb (Agents of SHIELD, Daredevil) and Jim Chory (Daredevil). John Cameron is also on board as an exec producer via his overall deal with FXP, marking his and Hawley's latest collaboration after the Golden Globe-winning anthology Fargo. Production on Legion will begin in March.