Before the first Suicide Squad film was released in August 2016, director David Ayer and star Will Smith were expected to return for a sequel. Filming was planned to begin in 2017 after the pair completed their work on the film Bright (2017).[54] Karen Fukuhara expressed her interest in fleshing out Tatsu Yamashiro / Katana's backstory in a sequel, though she also noted that if not, that could be in a spin-off film of her own.[55] In September, Ayer said the first film had been rated PG-13 because it had originally been envisioned that way by the studio, and an R-rating needed to be planned from the start of a production. He said that it would be worth "lobbying" to make a sequel R-rated, as he felt the first film had the "edge" and "attitude" of an R-rated film already.[56] Suicide Squad was released to a polarized response and was reported to have a difficult production, but the film grossed enough for Warner Bros. Pictures to fast-track development of a sequel.[57][58] Several spin-off films were also in development by December, including one featuring Smith as Deadshot. The project that was furthest along was Gotham City Sirens, an all-female team-up film with Margot Robbie planned to reprise her role as Harley Quinn. Ayer was set to direct and produce that film rather than Suicide Squad 2.[57]

Warner Bros. began searching for a new director for Suicide Squad 2, and was courting Mel Gibson by mid-February 2017.[58] Ruben Fleischer, Daniel Espinosa, Jonathan Levine, and David S. Goyer were also considered.[59][60] Adam Cozad entered negotiations to write the film a month later, at which point there was still no director attached to the project. It was described as being a priority for Warner Bros.[61] Script delays led to the planned filming start being pushed to mid-2018, at which point Gibson moved on from the project. Jaume Collet-Serra became the new frontrunner to direct in early July,[62] by which time both Smith and Robbie were set to reprise their roles.[62] Zak Penn had pitched a new story treatment for the film to Warner Bros.,[63] and wrote a draft of the script as a favor to the studio.[63][64] Later in July, Collet-Serra was hired to direct Disney's Jungle Cruise (2021) and withdrew from directing Suicide Squad 2 after deciding he would rather originate a new story than continue an existing franchise;[65] Collet-Serra went on to direct the DC Extended Universe (DCEU) film Black Adam (2022).[66]

In August, Jared Leto was expected to reprise his role as the Joker from the first film,[67] while production was not expected to begin until Smith completed his work on Aladdin (2019) and Gemini Man (2019) in late 2018.[68] The next month, Gavin O'Connor was chosen to direct the film and co-write it with his writing partner Anthony Tambakis, based on his own vision.[69][70] The character Black Adam was reportedly the main villain of O'Connor's script, with Dwayne Johnson already attached to that role for DC Films.[71][72] Michael De Luca joined the film as a producer in January 2018, working with the first film's producer Charles Roven.[73] David Bar Katz and Todd Stashwick were co-writing the film with O'Connor in June,[74] and they had completed their draft by that September.[75] O'Connor left the film by early October to focus on The Way Back (2020). This was reportedly out of frustration that Warner Bros. was already moving ahead with Birds of Prey (2020), a new Harley Quinn spin-off film with a similar story to the one he wrote for Suicide Squad 2.[76] During the development process, the character Deathstroke appeared in four or five different version of the script to fight Deadshot. Joe Manganiello was attached to reprise his role as Deathstroke from Justice League (2017), and the experience left him feeling that he would never portray the character again until he was asked to return for Zack Snyder's Justice League (2021).[77][78]

In October 2018, James Gunn was hired to write and possibly direct the next Suicide Squad film.[79] His deal with Warner Bros. closed following the completion of his exit settlement with The Walt Disney Company, after he was dismissed by Disney and Marvel Studios as director of Guardians of the Galaxy Vol. 3 (2023) in July 2018 when conservative commentators, such as Mike Cernovich, circulated controversial Twitter posts he made involving rape, pedophilia, AIDS, the Holocaust, bestiality and 9/11.[80] Warner Bros. had been interested in recruiting Gunn for the DCEU immediately after his dismissal by Disney[81] and asked him to make a new Superman film.[10][82] Gunn was uncertain if he wanted to take on Superman, so Warner Bros. told him that he could adapt any DC property he liked. He chose to make a Suicide Squad film, recalling that it was the one DC property he dreamed of adapting and had been jealous when Ayer's Suicide Squad film performed well.[10] Ayer supported Gunn's hiring as a "brave and smart move" and called him "the right man for the job". Dave Bautista, who starred in the Guardians of the Galaxy films for Gunn, expressed interest in appearing in his Suicide Squad film.[83]

One of the first things Gunn did when discussing the film with Warner Bros. was watch Suicide Squad for the first time. The studio said he could take or leave any elements he wanted from the first film, but they hoped that he would bring back Robbie as Harley Quinn.[24] The day after he was hired, Disney decided to reinstate Gunn as director of Guardians of the Galaxy Vol. 3. He discussed his new DCEU commitment with Marvel Studios President Kevin Feige, who encouraged him to "make a great movie" and agreed to delay production on Guardians until Gunn had completed work on the Suicide Squad sequel.[84] In January 2019, the film was officially titled The Suicide Squad and was scheduled for release on August 6, 2021.[85] The title was suggested by Gunn as a joke, but executives at Warner Bros. liked it.[86] At that time, Gunn was in negotiations to direct the film which was described as a relaunch rather than a direct sequel that would take the franchise in a new direction and feature a largely new cast. Roven and Peter Safran were set as producers, with Zack Snyder and Deborah Snyder as executive producers.[87] Safran, who produced the DCEU films Aquaman (2018) and Shazam! (2019), had pushed Gunn to take on the project and felt there was no better director to "bring together a disparate group of outsiders on a mission".[88]

Gunn wrote a treatment that was a few pages long,[16] and then quickly produced several drafts of the script that Warner Bros. was "extremely high" on.[89] He said the film was "its own thing", rather than a sequel or reboot;[90] it does not explicitly address the events of the first film or Birds of Prey,[91] but it also does not contradict them.[90] Warner Bros. asked Gunn to make the film PG-13, but he insisted on it being R-rated if he was going to direct it; the studio felt Gunn's involvement was "worth the trade-off" for the higher rating.[8] He took inspiration from John Ostrander's original 1980s run on the Suicide Squad comic books,[23] which he was drawn to because it was about a "bunch of loser, B-grade supervillains".[12] Safran described The Suicide Squad as a "gritty 1970s war movie combined with the brilliance of James Gunn's characters and comedy",[92] and Gunn was influenced by war films such as The Great Escape (1963), The Dirty Dozen (1967), Where Eagles Dare (1968), and Kelly's Heroes (1970).[10][23][93]

Already knowing the kind of story that he wanted to tell, Gunn's first step in writing the film was picking the characters for the Suicide Squad roster. He spent days going through the library of existing DC Comics characters and deciding which group would work well together. He wanted to create a blend of characters by having each feel like they were part of a different film genre.[16] The first new character that Gunn added to the roster was King Shark,[94] who was intended to appear in the first film before being replaced by Killer Croc.[95] Gunn sought to feature an animal on the team, and chose King Shark because he enjoyed the concept of a man-eating fish-human hybrid.[94] Other new characters that Gunn added include Polka-Dot Man, Peacemaker, and a female version of Ratcatcher.[96] He said one of the main differences between this film and the Guardians of the Galaxy films was that it would be unclear whether some Suicide Squad members would turn out to be good or bad, unlike the Guardians of the Galaxy who are portrayed as heroes despite their flaws.[90] Characters that were considered but ultimately rejected include Sportsmaster,[97] Dogwelder,[98] Bat-Mite,[23] Livewire, Punch and Jewelee, Black Spider, Deathstroke, Man-Bat, Plastique, Chemo, KGBeast, Solomon Grundy, Rainbow Creature, Gunhawk, Knockout, Killer Frost, Mr. Freeze,[99][100][101] and Yahya Abdul-Mateen II's Black Manta from Aquaman.[102] He did not consider using the Joker because he felt Amanda Waller would not have any use for the character,[103] and chose not to use Kite Man because he felt the character was already a punchline in the comics and would not feel fresh for the film.[104] Gunn also avoided characters like Bronze Tiger and Katana since they are antiheroes rather than villains.[105]

Gunn felt he was in a position, and had the responsibility, to take risks with the property and try make "an all-out entertaining film from start to finish that didn't play by the rules". This included "post-modern" aesthetic decisions such as creating sequences that showed the perspectives of Harley Quinn and Polka-Dot Man, adding an extended subplot where Harley Quinn is on her own away from the action, and adding title cards that segue between sequences.[9] These elements were written into the script,[16] including what Gunn referred to as "Harley-vision" where gory murders are depicted through Harley's "starry-eyed way of looking at life" by mixing "hearts and beautiful little things" with the blood that is coming out of the people Harley is killing. The "Harley-vision" visuals were inspired by a video game that Gunn helped develop called Lollipop Chainsaw (2012).[8]

He chose to make a Suicide Squad film, recalling that it was the one DC property he dreamed of adapting and had been jealous when Ayer's Suicide Squad film performed well[...]
The studio said he could take or leave any elements he wanted from the first film, but they hoped that he would bring back Robbie as Harley Quinn.[...]
the film was officially titled The Suicide Squad [...]
The title was suggested by Gunn as a joke, but executives at Warner Bros. liked it. [...]
was described as a relaunch rather than a direct sequel that would take the franchise in a new direction and feature a largely new cast[...]
He said the film was "its own thing", rather than a sequel or reboot;[90] it does not explicitly address the events of the first film or Birds of Prey,[91] but it also does not contradict them.[...]