Johnny Depp

James 'Whitey' Bulger

Joel Edgerton

John Connolly

Julianne Nicholson

Marianne Connolly

Dakota Johnson

Lindsey Cyr

Kevin Bacon

FBI Agent Charles McGuire

Benedict Cumberbatch

Billy Bulger

Peter Sarsgaard

Brian Halloran

Juno Temple

Deborah Hussey

Jesse Plemons

Kevin Weeks

David Harbour

John Morris

Adam Scott

FBI Agent Robert Fitzpatrick

Corey Stoll

Fred Wyshak

Bill Camp

John Callahan

Brad Carter

John McIntyre

Scott G. Anderson

Tommy King

Lonnie Farmer

DEA Agent Eric Olsen (Interrogator)

Erica McDermott

Mary Bulger

Owen Burke

Buddy Leonard

Lewis D. Wheeler

Jeremiah O'Sullivan

Jamie Donnelly

Mrs. Cody

David De Beck

Roger Wheeler

Gary Galone

State Captain

Rory Cochrane

Stephen Flemmi

James Russo

Agent Scott Gariola

Danae Nason

McGuire's Secretary

Thomas Philip O'Neill

FBI Wire Tech

Anthony Molinari

Charlie McTiernan

Declan Mulvey

Charlie's Friend

Bates Wilder

Agent James

Brian A. White

Prisoner

Tom Kemp

Father Mackey

Patrick M. Walsh

Michael Donahue

Naheem Garcia

DEA Agent

Cary 'Big Shug' Guy

Drug Dealer

Jack Neary

Barman

Arthur Hiou

Driver

Robert E. Walsh

Sr. FBI Official (voice)

W. Earl Brown

John Martorano

Jim Powers

The Mayor

Jeff Kamps

Walker

Susan Garfield

Press Photographer

Colleen Kelly

Marion Hussey (uncredited)