Scripts for both Justice League Part Two (or Justice League 2) and Justice League Part Three (a.k.a. Justice League 3) to follow Justice League/Zack Snyder's Justice League were ultimately never written and never had any writers assigned to them; however, Snyder had a plan for their stories and comic artist Jim Lee illustrated "breakdown boards" for them. As we all know, production was originally expected to commence after the release of Justice League/Zack Snyder's Justice League, but work on the second one halted after Snyder stepped down in May of '17, and it was pushed indefinitely that December in favor of a standalone Batman film. After Justice League proved to be a commercial disappointment and received mixed reviews from both critics and fans alike, D.C. and Warner Bros. decided to re-evaluate their strategy for the D.C.E.U. and transition from Snyder's vision, causing Snyder and his cast and crew to slowly begin leaking the details about his Justice League trilogy plans.

Please note: The following details are mostly based upon the storyboards that Snyder created with Jim Lee's help and were a very rough outline for his five- or six-film story arc. They were made from 2014 to '15 and, by the releases of both versions of Batman v Superman: Dawn of Justice, these storyboards became outdated and were abandoned as Snyder's vision evolved. However, they are on display at The Dreamscapes of Zack Snyder's Justice League Exhibition in downtown Dallas, Texas.

1. After teasing Darkseid in Zack Snyder's Justice League and Zack Snyder's Justice League: Justice Is Gray Edition, he would have been the main villain in Justice League Part Two.

2. Batman was going to die in Justice League 3.

3. Following a now-cut ending from Zack Snyder's Justice League, which originally featured the Green Lanterns John Stewart, Kilowog, and Tomar-Re, which was later repurposed to include both Stewart and the Martian Manhunter before it was cut out, members of the Green Lantern Corps were expected to appear in Justice League 2, including Hal Jordan. Producer Charles Roven was rumored to have an interest in having Mark Wahlberg portray the Corps' most famous member, though he was never officially cast in the role. In earlier scrapped ideas of Justice League Part 2 and 2A from '14 to 2015, Hal Jordan would have been introduced in the final Justice League film set in the "Knightmare" future. By '16, with those ideas having been partly scrapped and/or altered, it would seem that plans for Hal to also appear a bit earlier in Justice League 2 alongside the rest of the Green Lantern Corps were altered.

4. Snyder said that the scene in Batman v Superman: Dawn of Justice with crosses over Superman's corpse were a cryptic reference to events in Justice League Part Two.

5. The "Knightmare" would have been crucial to the plot. Snyder's plans for the "Knightmare" timeline and beyond were loosely inspired by the plot of the 2013 video game Injustice: Gods Among Us and Grant Morrison's '08-'09 D.C. crossover storyline "Final Crisis", as well as Geoff John's D.C. crossover storyline "Flashpoint".

6. While on the set of Star Wars: Episode IX - The Rise of Skywalker at Pinewood Studios - where Justice League/Zack Snyder's Justice League was also created - Kevin Smith met with some of the crew who worked on Snyder's films and learned about what the future would have held. He revealed that Justice League 2 was supposed to end in defeat, comparing it to films like Star Wars: Episode V - The Empire Strikes Back and Avengers: Infinity War.

7. Smith also said that Justice League 3 would have been set entirely in the post-apocalyptic "Knightmare" Earth seen in Bruce Wayne's dream in B.vS.D.o.J., with a rough synopsis of it being, "The heroes' final stand against Darkseid and the forces of Apokolips." Conversely, however, Snyder later stated that it would have been Justice League Part Two that would've been set in the "Knightmare" version of Earth.

8. Snyder planned to flesh out the past story between Batman and the Joker in Justice League 2 by exploring how Robin died, including flashbacks of how the Joker and Harley Quinn murdered Dick Grayson before burning down Wayne Manor and confronting Batman. His idea was that there was a moment inspired by the Last Supper with the Insurgency in which they all told each other stories out of the belief that they were all going to die the following day, with the Joker telling the story about how he and Harley killed Robin and Snyder said that the fight sequence would have been seen on-screen, showing that Robin did not go down and out without a fight.

9. Justice League Part Two would have featured Earth's downfall when Superman succumbed to the Anti-Life Equation, forcing the Flash to travel back to the past to prevent Superman's fall to darkness. The heroes would've fought Darkseid along with all of Earth's armies, navies, air forces, and marine corps united once more, including aircraft carriers, U.S. Army Special Forces members, the Atlanteans rising out of the oceans, and the Amazons leaving Themyscira.

10. The Flash would've been the only survivor of an attack by the Anti-Life-controlled Superman, and would only escape Superman through time travel.

11. At some point into Justice League 3, the time-traveling Flash would avert the apocalyptic future. Superman would become the League's leader and the central character following Batman's death at Darkseid's hands, sacrificing himself to save Lois. He would revert back to his classic red-and-blue suit and complete his five- or six-film character arc as Snyder intended since the release of Man of Steel, and united Humanity and all of Earth's armies, navies, air forces, and marine corps for the upcoming invasion. Aquaman would have led the Atlantean forces, while Superman would have led Humanity's forces against Darkseid. The Green Lantern Corps would have joined in the fight as well to fend off Darkseid's invading Apokoliptian forces. Wonder Woman's mother would've died in the war, with Diana succeeding her as the Queen of the Amazons. Aquaman would have united all the Kingdoms of the Sea and be recognized as the true king for uniting with the surface. Sometime after the end of the war, the Amazons would open up Themyscira to the rest of the world again. Barbara Gordon would succeed her father Jim after his retirement and take over for Batman until Superman and Lois's powerless son becomes the new Batman twenty years later.

In January 2019, Snyder released a t-shirt as a reward for donating to a crowdfunding campaign with all proceeds going toward the American Foundation for Suicide Prevention. His design, which resembles the Kabbalah Tree of Life, is said to contain the plot of his five-film arc including a planned Justice League trilogy within a mosaic of cryptic symbols and phrases. The reverse side of the shirt has a quote from Joseph Campbell, American literature professor famed for his creation of the Hero's Journey, which reads: "All the gods, all the heavens, all the hells, are within you". The Dreamscapes Of Zack Snyder's Justice League Exhibition in downtown Dallas revealed an outline for Justice League Parts 2 and 2A by Snyder, lettered by Geoff Johns, and with art by Jim Lee, showed costumes and props that were used in the additional photography for Zack Snyder's Justice League.

In February 2021, Snyder stated that as far as he knows, Warner Bros. currently has no interest in hiring him for further Justice League sequels or any D.C.E.U. movies overall, though he remains hopeful. He later revealed at Justice Con 2021 that he cast Wayne T. Carr as Green Lantern John Stewart and filmed footage for the film´s epilogue, but the studios turned this down.