The project, a co-production of Showtime and Sky Atlantic, is based on the Patrick Melrose series of semi-autobiographical novels written by Edward St. Aubyn. David Nicholls (Far From the Madding Crowd) is penning the TV adaptation.
Melrose skewers the upper class as it tracks the protagonist’s harrowing odyssey from a deeply traumatic childhood through adult substance abuse and, ultimately, toward recovery.
Williams will play Marianne, an acquaintance that Patrick (Cumberbatch) encounters during his playboy years in New York. She joins previously announced Jennifer Jason Leigh, Hugo Weaving and Anna Madeley.
Williams is best known for her role as Marnie in HBO’s Girls. This year, she earned critical praise for her role in the horror film Get Out, and she previously starred in the live television adaptation of Peter Pan as the title character.