Johnny Depp (James J. 'Whitey' Bulger), Joel Edgerton (John Connolly), Benedict Cumberbatch (William M. Bulger), Rory Cochrane (Steve Flemmi), Jesse Plemons (Kevin Weeks), Kevin Bacon (Charles McGuire), Peter Sarsgaard (Brian Halloran), Dakota Johnson (Lindsey Cyr), Corey Stoll (Fred Wyshak), Juno Temple (Deborah Hussey), Adam Scott (Robert Fitzpatrick), Julianne Nicholson (Marianne Connolly), David Harbour (John Morris), W. Earl Brown (John Martorano), Bill Camp (John Callahan), Mark Mahoney (Mickey Maloney), Jeremy Strong (Josh Bond), Brad Carter (John McIntyre), Scott Anderson (Tommy King), Lonnie Farmer (DEA-Agent Eric Olsen (Vernehmungsbeamter)), Mary Klug (Mutter Bulger), Erica McDermott (Mary Bulger), Luke Ryan (Douglas Cyr), Owen Burke (Buddy Leonard), Lewis D. Wheeler (Jeremiah O'Sullivan), Billy Meleady (Joe Cahill), Jamie Donnelly (Mrs. Cody), David De Beck (Roger Wheeler), David Conley (Officer Flynn), Ciaran Crawford (Irischer Nationalist), Anthony Molinari (Charlie McTiernan), Bates Wilder (Agent James)