The 2017 film Justice League had a troubled production history, undergoing major changes before and during production, including a change in directors. This resulted in the theatrical release being markedly different from its conception in pre-production and principal photography.

Justice League was directed by Zack Snyder for most of its production but he stepped down during post-production after his daughter's death. Joss Whedon completed the film as an uncredited co-director, overseeing script rewrites, reshoots, runtime cuts, and other changes driven by Warner Bros. Pictures and the reception of the DC Extended Universe (DCEU) films Batman v Superman: Dawn of Justice and Suicide Squad (both 2016). The theatrical release of Justice League was a commercial failure, and received mixed reviews.

When details surfaced about its troubled production, some expressed interest in the idea of releasing an alternate cut of the film that would be more faithful to Snyder's vision. This was later petitioned by audiences, some of the film's cast and crew, and other industry figures. Although Warner Bros. initially rejected the idea, Zack Snyder's Justice League was released in 2021, on HBO Max.

Original Snyder/Beall/Terrio script (2014–2016) Following the release of Man of Steel (2013), Snyder outlined the basis of the DC Extended Universe (DCEU), which centered around a five-film arc including Man of Steel, Batman v Superman: Dawn of Justice (2016) and a Justice League trilogy. As interpreted by Stephen M. Colbert of Screen Rant, the structure of the franchise would have been the "inverse" of the Marvel Cinematic Universe (MCU). Instead of solo films culminating in cross-over Avengers films, DC would primarily feature cross-over films with occasional solo films set at different points in time.

Snyder opted to have Batman v Superman: Dawn of Justice as the darkest in tone, and the following films be more hopeful in tone (Snyder described his original Justice League script written with Chris Terrio as "dark" and "scary"). Concept art revealed scenes involving Apokolips and the New Gods, and were noted as being heavily influenced by science fiction and the work of H. R. Giger. In cinematographer Fabian Wagner's first meeting with Snyder, Snyder informed him he wanted to depart from the "stylized, desaturated, super-high contrast looks of other [DCEU] films", hinting at a darker tone.

As revealed in 2024, Will Beall was hired to write a very early draft for the script of Justice League; some of its elements would be incorporated into Zack Snyder's Justice League. Beall's draft had the majority of the second act acting like a "little sort of coda" of the post-apocalyptic "Knightmare" future timeline that appeared in Batman v Superman: Dawn of Justice as a flashforward with the heroes and villains forced to team up, having lots of inspiration to Back to the Future Part II (1989).

In 2019, Snyder revealed part of Justice League would have seen Darkseid teleport into the Batcave and kill Lois Lane. This would eventually make Superman subject to the Anti-Life Equation and under Darkseid's control to take over Earth. In response, Batman and Cyborg would send Flash back in time to save Lois and Superman. This idea was never filmed, however, it was partly referenced in Zack Snyder's Justice League, as a vision from Cyborg.

The "Snyder Cut" (2016–2017) Batman v Superman: Dawn of Justice received generally negative reviews from critics, and mixed reviews from audiences. Criticism centered around its dark tone, lack of humor, and slow pace. This caused Warner Bros. and Snyder to reevaluate upcoming DCEU films, particularly Suicide Squad and Justice League. As such, Snyder and Terrio's original plan to make DCEU films become progressively lighter and more positive in tone was abandoned, and the "dark and weird" Justice League was rewritten to be more light hearted. Snyder cited this version to be a mixture between his original idea and the light hearted tone requested by Warner Bros.

In May 2016, Warner Bros. hired Jon Berg and Geoff Johns to oversee the DCEU, including Justice League rewrites. Batman actor Ben Affleck was hired to rewrite and serve as an executive producer on Justice League and help ensure continuity between the film and The Batman, which he was expected to star in and direct at the time. Alfred Pennyworth actor Jeremy Irons said Snyder's script was simpler, smaller and more linear than Batman v Superman: Dawn of Justice. The rewrites resulted in delays to filming, which began in May 2016.

Principal photography was shot entirely on 35 mm film and wrapped in December 2016. Months later, cuts of the film were shown to Warner Bros. executives and Snyder's friends and family. A final run-time and picture lock were achieved, though the cuts had incomplete VFX shots and partial audio mixing. Composer Tom Holkenborg completed the film's score. Snyder said that the film contained multiple cuts which needed only "a few CG tweaks" and the final version would be approved by Warner Bros. Screenwriter Mark Hughes reported that the final cut was mostly done, while The Telegraph cited a VFX expert as estimating that the studio would need another $30–40 million to finish the film. This mostly finished version of Justice League is what is often referred to as the "Snyder Cut". Citing unnamed sources of Justice Leagues crew "at various levels", Kevin Smith described the state of the cut as:

"When people hear 'Snyder Cut', they think an extended cut that's finished. The 'Snyder Cut' that I've heard of was never finished. It was a [film] that people in production could watch and fill in the blanks. It was certainly not meant for mass consumption".

This version of the "Snyder Cut" was 214 minutes (over three-and-a-half hours) while the assembly cut was nearly five hours long. The basic story from Snyder's Justice League was largely maintained for the theatrical release but dozens of additional scenes related to backstories, mythos, worldbuilding elements, new characters, and teases for upcoming films were removed. This included the introductions of Darkseid, DeSaad, Nuidis Vulko, Ryan Choi, Elinore Stone, Iris West, and Martian Manhunter. Sequences related to the on-screen prominence of Lex Luthor, Silas Stone, Mera, Lois Lane, and Ares were reduced, as was the time-travel plot in Snyder and Terrio's original draft. The theatrical cut instead opted to emphasize the involvement of Flash, Aquaman, and Cyborg. The depiction of Aquaman in the film and in Aquaman (2018) was said to be consistent with Snyder's intended vision.

According to insider reports, Warner Bros. executives noted the effort to lighten the Snyder cut's tone but labelled it "unwatchable", citing a lack of humor. Neil Daly, who oversaw the film's test screenings, said test audiences ranked Batman and Superman the lowest of the main cast. In 2021, David Brenner, one of the film's editors, claimed Warner never screened Snyder's cut to test audiences and instead viewed a 2 and a half hour cut, after which, they began initiating further rewrites. The first two trailers for Justice League used footage from the "Snyder Cut", and were subject to mixed reception.

#ReleaseTheSnyderCut movement

Immediately after the theatrical release of Justice League, fans created an online petition to release the "Snyder Cut" that gained more than 180,000 signatures. The movement, which uses the hashtag #ReleaseTheSnyderCut on social media, began before fans had any knowledge that a cut of Snyder's Justice League film actually existed in any capacity. The movement was ignited by the divisive reaction toward the theatrical cut, knowing that Snyder left directorial duties and the final cut of the film in the hands of Joss Whedon and the assumption that Whedon created an inferior film. The circumstances have been compared to a similar situation with the film Superman II (1980). Both Justice League and Superman II feature a director that was replaced, for different reasons, before completion of a film, which led to a second director coming in and making substantial changes to the tone of each film. Although the reasoning behind each director's departure differs, Richard Donner was able to complete his Superman II cut in 2006. Some assumed that an alternate cut of Justice League was inevitable because historically several of Snyder's films have been re-released as extended cuts for home media (Watchmen (2009), Batman v Superman: Dawn of Justice) which are seen by some critics as superior to the original version. In July 2018, The Wall Street Journal reported that Warner Bros. had no plans of releasing an alternate cut of Justice League. In November 2019, both The Hollywood Reporter and Variety independently reported Warner had no plans to release the "Snyder Cut", with the latter quoting an inside source as saying, "That's a pipe dream. There's no way it's ever happening".

Theatrical cut (2017)

After disapproving of the direction of the "Snyder Cut", Warner Bros. and Geoff Johns hired filmmaker Joss Whedon to re-write the script and help with extensive re-shoots. (However, he may have been hired earlier than reported, to join a larger writer's room.) Whedon had gone to Warner Bros. with a pitch for a Batgirl film. Johns accepted his pitch and was working with him on developing that film. Johns then saw this as an opportunity to help with additional rewrites and reshoots for Justice League. Dismissing reports that he requested Whedon's help, Snyder did hope that Whedon could give him some help by writing some "cool scenes", but only had one conversation about the studio's notes with Whedon. Soon, the studio gave Whedon more power as he was also given power to help direct reshoots. Finding anguish rather than relief on their work, when Snyder and his wife left the project after their daughter's death, Whedon took over as director and directed reshoots for approximately 55 days. Then-Warner Bros. CEO Kevin Tsujihara mandated that Justice Leagues length was not to exceed two hours, something the studio had been pushing for throughout principal photography, but Snyder himself never took seriously, saying it was near impossible to tell his story in two hours. The film company also reportedly decided not to push back the release date (which would have allowed the filmmakers more time to properly complete Justice League), partly so that executives could keep their annual bonuses, and partly because they were concerned that AT&T might dissolve the studio after an upcoming merger, which might result in the incomplete film getting scrapped altogether.

Snyder may also have turned down an offer to delay the release date. He was expected to film the scenes that Whedon re-wrote, and they were working together to fix the film in accordance with the studio's requests when Snyder's daughter, Autumn Snyder, died by suicide in March 2017. He continued to work on Justice League for two months after the tragedy to distract himself, before finally stepping down in May 2017. His wife Deborah Snyder who was producing Justice League also stepped away from the project. Some reports, however, say that Snyder may have been quietly fired from the project in January or February 2017, a month or two before his daughter's suicide and several more before his official departure from the project. Once Snyder left, Whedon assumed full control over the completion of the theatrical cut of Justice League. Warner Bros. COO Toby Emmerich said at the time:

"The directing is minimal and it has to adhere to the style and tone and the template that Zack set. We're not introducing any new characters. It's the same characters in some new scenes. He's handing the baton to Joss, but the course has really been set by Zack. I still believe that despite this tragedy, we'll still end up with a great movie".