Thousands of years ago, Steppenwolf and his legions of Parademons attempted to take over Earth with the combined energies of three Mother Boxes. They were foiled by a unified army that includes the Olympian Gods, Amazons, Atlanteans, mankind and a Green Lantern. After repelling Steppenwolf's army, the Mother Boxes were separated and hidden in locations on the planet. In the present, mankind is in mourning over Superman, whose death triggers the Mother Boxes to reactivate and Steppenwolf's return to Earth. In an effort to regain favor with his master, Darkseid, Steppenwolf aims to gather the boxes to form "The Unity", which will destroy Earth's ecology and terraform it in the image of Steppenwolf's homeworld.
Steppenwolf retrieves the Mother Box from Themyscira, prompting Queen Hippolyta to warn her daughter Diana of Steppenwolf's return. Diana joins Bruce Wayne in his attempt to unite other metahumans to their cause, with Wayne going after Arthur Curry and Barry Allen, while Diana tries to locate Victor Stone. Wayne fails to persuade Curry, but manages to recruit an enthusiastic Allen onto the team. Although Diana fails to convince Stone to join, he agrees to help them locate the threat if he discovers their location. Stone later joins the team after his father Silas and several other S.T.A.R. Labs employees are kidnapped by Steppenwolf seeking to acquire the Mother Box from mankind.
Steppenwolf attacks Atlantis to retrieve the next Mother Box, forcing Curry into action. The team receives intel from Commissioner James Gordon leading them to Steppenwolf's army, based in an abandoned facility under Gotham Harbor. Although the group manages to rescue the kidnapped employees, the facility is flooded during combat, which traps the team until Curry helps delay the flood so they can escape. Stone retrieves the last Mother Box, which he had hidden, for the group to analyze. Stone reveals that his father used the Mother Box to rebuild Stone's body after an accident almost cost him his life. Wayne decides to use the Mother Box to resurrect Superman, not only to help them fight off Steppenwolf's invasion, but also to restore hope to mankind. Diana and Curry are hesitant about the idea, but Wayne forms a secret contingency plan in case Superman returns as hostile.
Clark Kent's body is exhumed and placed in the amniotic fluid of the genesis chamber of the Kryptonian ship alongside the Mother Box, which in turn activates and successfully resurrects Superman. However, Superman's memories have not returned, and he attacks the group after Stone accidentally launches a projectile at him. On the verge of being killed by Superman, Batman enacts his contingency plan: Lois Lane. Superman calms down and leaves with Lane to his family home in Smallville, where he reflects and his memories slowly come back. In the turmoil, the last Mother Box is left unguarded and Steppenwolf retrieves it with ease. Without Superman to aid them, the five heroes travel to a village in Russia where Steppenwolf aims to unite the Mother Boxes once again to remake Earth. The team fights their way through the Parademons to reach Steppenwolf, although they are unable to distract him enough for Stone to separate the Mother boxes. Superman arrives and assists Allen in evacuating the city, as well as Stone in separating the Mother Boxes. The team defeats Steppenwolf, who, overcome with fear, is attacked by his own Parademons before they all teleport away.
After the battle, Bruce and Diana agree to set up a base of operations for the team, with room for more members. Diana steps back into the public spotlight as a hero; Barry acquires a job in Central City's police department, impressing his father; Victor continues to explore and enhance his abilities with his father in S.T.A.R. Labs; Arthur returns to Atlantis; and Superman resumes his life as reporter Clark Kent. In a post-credits scene, Lex Luthor escapes from Arkham Asylum and then recruits Slade Wilson to form their own league.
- Will Arnett as Bruce Wayne / Batman, A wealthy socialite, and the owner of Wayne Enterprises. He dedicates himself to protecting Gotham City from its criminal underworld as a highly trained, masked vigilante equipped with various tools and weapons.
- Channing Tatum as Clark Kent / Superman, A member of, and inspiration for, the Justice League. He is a Kryptonian survivor, and a journalist for the Daily Planet based in Metropolis. In Justice League, Superman was portrayed as more optimistic and hopeful.
- Cobie Smulders as Diana Prince / Wonder Woman, An antiquities dealer, acquaintance of Wayne, and an immortal Amazonian warrior, who is the crown princess of Themyscira and daughter of Hippolyta and Zeus. She is endowed with metahuman attributes and abilities inherited from her parents.
- Adam DeVine as Barry Allen / The Flash, A Central City University student, who can move at superhuman speeds with his ability to tap into the Speed Force.
- Jason Momoa as Arthur Curry / Aquaman, The heir to the throne of the undersea nation of Atlantis. His metahuman aquatic abilities and physical attributes originate from his Atlantean physiology.
- Kevin Hart as Victor Stone / Cyborg, A former college athlete who, after being cybernetically reconstructed after a nearly fatal car accident, is turned into a techno-organic being enhanced by reactive, adaptive biomimetic alien technology. His enhancements include the abilities of flight, variable weaponry and technopathy.
- Kristen Bell as Lois Lane, An undaunted and compassionate award-winning journalist for the Daily Planet and the love interest for Kent.
- Ralph Fiennes as Alfred Pennyworth, Wayne's butler, chief of security, and trusted confidant.
- Tom Kenny as Martha Kent, Kent's adoptive mother.
- Dee Bradley Baker as Hippolyta, Diana's mother and Queen of the Amazons.
- Héctor Elizondo as James Gordon, The Commissioner of the Gotham City Police Department, and close ally of Batman.
- Steve Coogan as Steppenwolf, An alien military officer from Apokolips who leads an army of Parademons and is searching for the three Mother Boxes held on Earth. The character is described as "old, tired" and trying to find a way to escape his role of servitude under Darkseid.
In January 24, 2020. Chris McKay a set to be released on April 1, 2022 at Warner Bros. Pictures.
The LEGO Justice League Movie was released on DVD on July 4, 2022.