Joaquin Phoenix
Arthur Fleck

Lady Gaga
Lee Quinzel

Brendan Gleeson
Jackie Sullivan

Catherine Keener
Maryanne Stewart

Zazie Beetz
Sophie Dumond

Steve Coogan
Paddy Meyers

Harry Lawtey
Harvey Dent

Leigh Gill
Gary Puddles

Ken Leung
Dr. Victor Liu

Jacob Lofland
Ricky Meline

Bill Smitrovich
Judge Herman Rothwax

Sharon Washington
Debra Kane

Alfred Rubin Thompson
Ernie Bullock

Connor Storrie
Young Inmate

Gregg Daniel
Music Teacher

Mac Brandt
Arkham Guard

George Carroll
Arkham Guard

John Lacy
Arkham Guard

Tim Dillon
Arkham Guard

Wayne Dehart
E Ward Inmate

Troy Fromin
E Ward Inmate

Ajgie Kirkland
E Ward Inmate

Jimmy Walker Jr.
E Ward Inmate

Toney Wilson
E Ward Inmate

June Carryl
Dr. Louise Beatty

Don McManus
Paddy Meyers' Producer

G.L. McQueary
Head Bailiff

Angela D. Watson
Jury Foreman

Murphy Guyer
White Chapel Minister

Carson Higgins
Junior Associate

Gattlin Griffith
Masked Joker Driver

Hudson Oz
Joker Doppelganger

Ray Lykins
Victim's Dad

Will Ropp
Joker Fan #1

Ashton Moio
Joker Fan #2

Brian Donahue
Additional Guard

Mike Houston
Additional Guard

Jess King
Additional Guard

Jimmy Smagula
Additional Guard

Stephen Stanton
Stan L. Brooks (voice)

Martin Kildare
News Anchor

Laurie Dawn
Reporter

Dominiqué Williams-Blair
Reporter

Barry Bonder
Reporter

Kaylah Sharve' Baker
Back-up Singer

Ashley Levin
Back-up Singer

Celeste Butler
Back-up Singer

Casey Burke
Girl #1 (uncredited)

Troy Metcalf
Music Room Inmate #1 (uncredited)

Ben van Diepen
Music Class (uncredited)

Karen Teliha
B Ward Music Class Patient #14 (uncredited)