Joaquin Phoenix as Arthur Fleck

Lady Gaga as Lee Quinzel

Brendan Gleeson as Jackie Sullivan

Catherine Keener as Maryanne Stewart

Zazie Beetz as Sophie Dumond

Steve Coogan as Paddy Meyers

Harry Lawtey as Harvey Dent

Leigh Gill as Gary Puddles

Ken Leung as Dr. Victor Liu

Jacob Lofland as Ricky Meline

Bill Smitrovich as Judge Herman Rothwax

Sharon Washington as Debra Kane

Alfred Rubin Thompson as Ernie Bullock

Connor Storrie as Young Inmate

Gregg Daniel as Music Teacher

Mac Brandt as Arkham Guard

George Carroll as Arkham Guard

John Lacy as Arkham Guard

Tim Dillon as Arkham Guard

Wayne Dehart as E Ward Inmate

Troy Fromin as E Ward Inmate

Ajgie Kirkland as E Ward Inmate

Terrance T.P. Polite as E Ward Inmate

Jimmy Walker Jr. as E Ward Inmate

Toney Wilson as E Ward Inmate

June Carryl as Dr. Louise Beatty

Don McManus as Paddy Meyers' Producer

G.L. McQueary as Head Bailiff

Angela D. Watson as Jury Foreman

Murphy Guyer as White Chapel Minister

Carson Higgins as Junior Associate

Gattlin Griffith as Masked Joker Driver

Hudson Oz as Joker Doppelganger

Ray Lykins as Victim's Dad

Will Ropp as Joker Fan #1

Ashton Moio as Joker Fan #2

Emilio Rojas as Joker Fan #3

Joe Spinney as Police Escort

Richard Busser as Additional Guard

Brian Donahue as Additional Guard

Mike Houston as Additional Guard

Jess King as Additional Guard

Jimmy Smagula as Additional Guard

Stephen Stanton as Stan L. Brooks (voice)

Martin Kildare as News Anchor

Laurie Dawn as Reporter

Steven X. Greenfield as Reporter

Dominiqué Williams-Blair as Reporter

Barry Bonder as Reporter

Kaylah Sharve' Baker as Back-up Singer

Ashley Levin as Back-up Singer

Celeste Butler as Back-up Singer

Alex Wesley Smith as Music Room Pianist

Robert Loftus as Arkham Guard (uncredited)

Casey Burke as Singer (uncredited)