In the aftermath of 's death, intelligence officer Amanda Waller convinces the US Government to greenlight Task Force X, a response team of criminals and supervillains. The team will be used to combat metahuman threats, under Waller's control via nanite bombs implanted in each criminal's neck, which can be remotely detonated if they try to rebel or escape. If successful, they will have their sentences shortened.
Dr. June Moone, an American archaeologist, becomes possessed by demonic witch Enchantress. Waller can control the Enchantress by seizing her magical heart, which wounds her if it is struck. Waller's subordinate Colonel Rick Flag is in love with Moone, and is made a member of Task Force X. However, Enchantress betrays Waller, conquering Midway City, transforming humans into monsters, and summoning her brother Incubus to destroy mankind.
Task Force X is formed to stop Enchantress, using six inmates from Deadshot, who wants to reunite with his daughter Zoe; Harley Quinn, a former psychiatrist-turned-girlfriend of Gotham crime lord Joker; Australian thief Captain Boomerang; pyrokinetic ex-gangster El Diablo; mutant cannibal ; ; and mercenary Slipknot. The team are led by Flag and joined by his associate Katana, a Japanese swordswoman.
Upon arrival in Midway City, the team's helicopter is shot down, forcing them to travel on foot. Boomerang convinces Slipknot to take off, believing the bombs are a ruse, but Flag kills Slipknot when he tries to escape, proving Boomerang's theory false. Scaling a skyscraper, the team discover Waller is their mark, trying to cover up her involvement in Enchantress' revolt. Meanwhile, the Joker learns of Harley's predicament, locates A.R.G.U.S. scientist Dr. Van Criss and blackmails him into disabling Harley's bomb.
As Waller and the squad await helicopter extraction, the Joker intervenes, disables Harley's bomb, and helps her escape. Waller shoots down the Joker's helicopter, though Harley survives and rejoins the squad, believing the Joker is dead. Enchantress captures Waller to regain her heart. Deadshot finds Waller's top-secret files and discovers Flag's relationship with Moone. The team abandon Flag, sharing a drink in an abandoned bar, where El Diablo reveals his powers and criminal lifestyle led to the deaths of his family. Flag relieves the squad of their mission, but realizing they have the opportunity to prove themselves, the group set out to save the city.
The squad attack Enchantress, while Killer Croc and Flag's platoon of Navy SEALs plant a bomb beneath the subway to kill her brother. El Diablo embraces his pyrokinesis, sacrificing himself to maneuver and keep Incubus in the right spot. Enchantress invites the squad to join her, and Harley pretends to be tempted to get close enough to cut out Enchantress's heart. Flag crushes her heart, killing her and releasing Moone from her control. Waller deducts ten years off each squad member's sentence and fulfill their requests (except for Boomerang, who is instead detained). The Joker, alive, breaks into Belle Reve and rescues Harley.
In a mid-credits scene, Waller meets with Bruce Wayne, who agrees to protect her from the legal consequences of the events in Midway City in exchange for government files on the growing metahuman community. He reveals his plans to contact the heroes in the file, including Flash and Aquaman, in order to build his own superhero team. She advises him to stop working late nights, implying she knows Bruce is Batman. In response, he tells Waller to shut down Task Force X or he and his "friends" will do it for her.
Will Smith as Floyd Lawton / Deadshot:
An expert marksman and assassin. A mercenary by day and a concerned father by night, Deadshot is a conflicted criminal who enjoys the hunt but still tries to do right by his young daughter. Smith was simultaneously offered to appear in Suicide Squad and Independence Day: Resurgence, the sequel to Independence Day which he starred in. Smith opted to portray Deadshot, saying that the choice was "nothing about the qualities of the movie—but the choice of trying to go forward versus clinging and clawing backwards."
Jared Leto as The Joker:
A psychopathic crime boss and the nemesis of Batman. Leto described his role as "nearly Shakespearean" and a "beautiful disaster of a character;" about portraying the villain, he stated, "I took a pretty deep dive. But this was a unique opportunity and I couldn't imagine doing it another way. It was fun, playing these psychological games. But at the same time it was very painful." Leto never broke character throughout filming, with Smith going as far as stating he never met him. In preparation for the role, Leto spent his time alone, listened to gospel music from the 1920s—commenting he senses "Joker may be much older than people think"—and read literature on shamanism. Influences for the character's appearance include the work of Alejandro Jodorowsky. The Joker's tattoos were added by Ayer, who believed it gave the character a modernized gangster look. David Bowie was also cited as an influence on the character by Leto.
Margot Robbie as Dr. Harleen Quinzel / Harley Quinn:
A former psychiatrist at Arkham Asylum seduced by the Joker into becoming his crazed partner-in-crime. Producer Richard Suckle described the character as, "a fan fave. Funny, crazy, scary. ... You can't come up with enough adjectives to describe all the different things you see her do." Robbie described Quinn as one of the Squad's most manipulative members and her relationship with Joker as "incredibly dysfunctional," adding that Quinn is, "mad about him—like, literally, mad. She's crazy. But she loves him. And it's a really unhealthy, dysfunctional relationship. But an addictive one."
Joel Kinnaman as Rick Flag:
The heroic, military leader of the Task Force X. A West Point graduate and Green Beret colonel who leads the Suicide Squad in the field. He is all business and executes Amanda Waller's orders but does not always agree with her goals or her methods. Tom Hardy was previously cast in the role but was forced to drop out because of scheduling conflicts.
Viola Davis as Amanda Waller:
The government official who gives out the Squad's orders. Ambitious and devious, she has big plans and intends to let no metahuman or military protocol get in her way. Davis stated she is fascinated by the character, singling out her psychology and strength and describing her as a "powerful black woman, hard, ready to pick up a gun and shoot anyone at will." She described Waller as "relentless in her villainy" and noted that her powers are "her intelligence and her complete lack of guilt."
Jai Courtney as George "Digger" Harkness / Captain Boomerang:
A thief who uses deadly boomerangs, described as rugged, unpredictable and mouthy. About his role, Courtney stated, "he is an absolute bogan, in the purest sense. David Ayer's first instruction was, 'find your inner dirtbag'."
Jay Hernandez as Chato Santana / El Diablo:
A former Los Angeles gang member who has metahuman powers that allow him to summon flames, and transform himself into a monstrous fire demon-like entity. He has squelched his fire-conjuring powers to a solitary flame as penance for the horrors he inflicted on those he loved. Hernandez set his character apart from his teammates as he "just wants to stay out of the fight," while "most of are happy to get out there and kill people."
Adewale Akinnuoye-Agbaje as Waylon Jones / Killer Croc:
A cannibalistic metahuman criminal who suffers from a regressive atavism which caused him to develop reptilian features. Being a meta-human, he possesses near superhuman strength, high endurance, and the capacity to breathe underwater. His skin allows him to withstand high caliber weapons and skin abrasion. Akinnuoye-Agbaje described the character as "a cannibal with rage issues."
Cara Delevingne as Dr. June Moone / Enchantress:
An archaeologist who is possessed by an ancient evil force that transforms her into a host of a powerful sorceress, when summoned. Unleashed after a long period of imprisonment, the entity draws the attention of Waller. Delevingne described Moone as "an adventure-seeker who's always wanted some excitement" and Enchantress as "a feral being." Originally, the film was going to feature the revelation that Enchantress was being controlled by Steppenwolf, the main antagonist of Justice League (2017), but this was scrapped after the Justice League story changed.
Ike Barinholtz as Capt. Hunter Griggs:
An officer at Belle Reve's Special Security Barracks, the black site where the government imprisons the squad.
Scott Eastwood as "GQ" Edwards:
A Navy SEAL Lieutenant who assists Flag during the squad's mission. After working with actor Shia LaBeouf on Fury, Ayer originally sought him out for the role, but the studio was not interested in the actor.
Adam Beach as Christopher Weiss / Slipknot:
A man who can climb anything.
Karen Fukuhara as Tatsu Yamashiro / Katana:
A volunteer heroic member of the Task Force X, who acts as Rick Flag's bodyguard. She is a widowed expert martial artist and swordswoman. Katana mourns her husband's death and wields the Soultaker Blade, a mystical weapon capable of trapping the souls of its victims; the artifact that holds her husband's soul. As she is not a criminal, she does not have a micro-bomb implant. Fukuhara stated that Katana "has morals and codes. She can also slice through hundreds of people without taking a breath."
Ben Affleck appears as Bruce Wayne / Batman, and Ezra Miller appears as Barry Allen / The Flash, both reprising their roles from Batman v Superman: Dawn of Justice with Miller's being a cameo role; while Jason Momoa makes a brief photographic appearance as Arthur Curry / Aquaman.Alain Chanoine portrays Incubus, the brother of Enchantress, who possesses the body of a businessman in Midway City in order to have a physical form. Jim Parrack and Common appear as the Joker's henchmen, Jonny Frost and Monster T, respectively. David Harbour portrays government official Dexter Tolliver (based on a DC character called Derek Tolliver), Alex Meraz portrays Navy SEAL Gomez, and Matt Baram portrays Dr. Van Criss, a scientist at Wayne Enterprises' branch Van Criss Laboratories. Shailyn Pierre-Dixon plays Zoe Lawton, Deadshot's daughter, and Corina Calderon plays Grace Santana, Diablo's wife. David Ayer, writer and director of the film, makes a cameo appearance as a Belle Reve officer.