Joaquin Phoenix: Arthur Fleck, Joker

Robert De Niro: Murray Franklin

Zazie Beetz: Sophie Dumond

Frances Conroy: Penny Fleck

Brett Cullen: Thomas Wayne

Shea Whigham: Detective Burke

Bill Camp: Detective Garrity

Glenn Fleshler: Randall

Leigh Gill: Gary

Josh Pais: Hoyt Vaughn

Rocco Luna: Gigi Dumond

Marc Maron: Gene Ufland

Sondra James: Dr. Sally

Murphy Guyer: Barry O'Donnell

Douglas Hodge: Alfred Pennyworth

Dante Pereira-Olson: Bruce Wayne

Carrie Louise Putrello: Martha Wayne

Sharon Washington: Social Worker

Hannah Gross: Young Penny