Justice League is the sixth film in the DC Extended Universe, and is the final film of phase one.
Lance Reddick as J'onn J'onzz/Martian Manhunter
Ian Somerhalder as Kal-El/Clark Kent/Superman
Ben Affleck as Bruce Wayne/Batman
Gal Gadot as Diana of Themyscira/Wonder Woman
Chris Pine as Bartholomew "Barry" Allen/The Flash
Alex O'Loughlin as Harold "Hal" Jordan/Green Lantern
Ron Perlman as the voice of Imperium Prime
Amy Adams as Lois Lane (cameo)
Hugh Laurie as Alfred Pennyworth (cameo)
Emma Stone as Iris West (cameo)
Gary Oldman as Captain Darryl Frye (cameo)
Chris Pratt as Steve Trevor (cameo)
Melissa McCarthy as Etta Candy (cameo)
Diane Kruger as Carol Ferris (cameo)
Michael C. Hall as Alexander "Lex" Luthor (cameo)
Clark Kent has a dream where a large space ship destroys two planets and then begins to head for Earth. He thinks he wakes up after this, but then sees a green figure floating in front of him. The figure comes in to the light, revealing it to be the Martian Manhunter, as he shows Clark visions of Batman, Flash, Green Lantern and Wonder Woman. Manhunter then gives Clark a simple order: find them. Clark then wakes up for real, and wonders what just happened.
Meanwhile, Bruce Wayne is chasing after a man who beat up someone for seemingly no reason. He catches up to the man on a roof top, with the man yelling about how "they're coming". Bruce demands to know who "they" are, with the man responding that they are the Imperium and that they will conquer the world. Bruce starts to walk closer to the man, whose head turns in to the upper half of a white, worm-like creature. It attempts to attack Bruce, but Bruce knocks its lower half off balance, knocking the full thing off the building. Bruce then looks down and sees the creature' true form laying dead.
Bruce then takes a few steps back to think about what just happened, but is snapped out of it when he hears a voice. Bruce looks up and sees Superman floating above him. Bruce asks Superman if he had anything to do with this, but Clark claims he doesn't and that he actually fought one of those things in Metropolis. Clark then asks Bruce to come with him, only to be killed by the real Superman. The fake Superman drops down and turns in to another one of the creatures. Clark then says that he needs Bruce's help, with Bruce demanding to know why. Clark then tells Bruce about his dream, with Bruce asking who's next.
Cut to Central City, where a man is holding a group of people hostage. Barry shows up and punches the man before helping the hostage up, only for the hostage and the criminal to turn in to the creatures. The creatures attempt to kill Barry, but Barry manages to escape. The creatures then fuse in to one being and come after Barry again, only for Barry to close a door on the creature's arm, ripping it off. The creature then bursts through the door, and Barry punches it in the chest so hard its chest ruptures and spills purple ooze everywhere before the thing dies. Barry then steps back in shock, but is snapped out of it when he hears Superman's voice. He turns to see Batman and Superman, with Superman assuring Barry that he didn't just commit murder, as the things have no humanity in them.
Later in Washington, Wonder Woman is also fighting off these things, who apparently pretended to be two women calling for help. Diana manages to defeat the creatures, stabbing one and blowing up the other with electricity. The other three heroes then show up and explain everything to her. Diana asks about the Manhunter, claiming that he could come in handy. Superman says that he's not sure why but he thinks he knows where Manhunter is, sending Wonder Woman and Flash to the location, while himself and Batman search for Green Lantern.
Flash and Wonder Woman speak to each other about what they do and where they came from while on their way to find Manhunter. When they eventually make it there, they are surprised at the fact it's a Military base. Diana and Barry break in to the base and begin searching for Manhunter, with Barry commenting on the fact no one seems to be here. That is until they begin to hear screaming. They both run to the location, with Diana making it there second. They find Manhunter, who is being tortured by the creatures. One of the creatures then asks Manhunter how he feels about the fact the Imperium destroyed his home planet Mars and killed his family, with Manhunter telling the creature to die. It is then about to kill Manhunter, but is stopped by Barry, who knocks the thing over and then uses its own torture device on it, which makes the thing blow up.
Barry lets the Manhunter down, with Diana about to shake Manhunter's hand, but Manhunter then uses laser vision on her, blowing her up and revealing her to be a creature. The real Diana then shows up, with Barry about to fight her, but Manhunter telling him to stop and that she's real. Barry asks how he knows with Manhunter revealing he can read minds. Manhunter then picks up a marker and draws an X on all of their heads so that they can't be tricked again. The three are about to get out of the base, but are then surrounded by army soldiers and tanks, who all shape shift in to the creatures.
Back with Superman and Batman, Bruce has gotten the same idea as Manhunter, as he draws an X on Clark's head and his own. The two then have a short conversation where they reveal they both know each other's secret identities, but are then stopped when they see something crash. They both charge for it, finding Green Lantern laying in a crator. Clark wakes Lantern up, with Lantern panicking before calming down a bit and saying that they're too late and that the Imperium is coming.
Meanwhile, Barry, Diana and Manhunter are fighting off the Imperium, with it ending when Manhunter uses his laser vision again and destroys them all. Barry asks Manhunter for a high five, but Manhunter has no clue what a high five is, so Barry just puts his hand back down. Manhunter then says that they should group with the other heroes, but then stops in his tracks. Manhunter looks around and then tells Barry and Diana to get back in the base, Barry tries to argue, but Manhunter yells for them to get in now. After this, they obey, with Manhunter following and covering the base's entrance with a boulder.
They all make it back to the room where they first found Manhunter, which has a massive television screen in it. Barry once again tries to ask what's going on, but is stopped when a loud voice addresses everyone on Earth, as the large screen fills with a live video of a purple creature with tentacles, who Manhunter refers to as "Imperium Prime".
Imperium Prime continues his speech, as it shows everyone listening to it, Clark, Bruce, Hal, Lois Lane, Alfred Pennyworth, Iris West, Darryl Frye, Steve Trevor, Etta Candy, and Carol Ferris. Prime's speech lists off the planets he's taken over, and the races he's wiped out, before ending it saying that Earth is next and that no one can stop him. The Imperium war fleet then show up as in every city people see ships above them and are panicking.
Back with Barry, Diana and Manhunter, Barry is arguing with Manhunter, with Manhunter claiming that he can't stop them but Barry yelling that he can and he just doesn't want to. The argument ends when Diana tells the both of them that arguing solves nothing, and that if they unite with the others they'll be able to take down every last one of the Imperium. Barry and Manhunter then look at each other and nod before running off.
Meanwhile, Hal, Bruce and Clark are waiting for the Imperium to do something, which they do as they beam down their soldiers who begin attacking the city. The three then work together to take down as many Imperium as they can, with Manhunter, Barry and Diana joining them later on. Manhunter then tells the others that if they take down Imperium Prime's ship then the rest will follow and all the Imperium will die. Clark then asks which one is Imperium Prime's, with Manhunter looking around and saying that the ship isn't close by. After hearing this, Barry runs at top speeds all around the world and says that the biggest ship is in Gotham.
Manhunter then flies off and makes his way to Gotham, where he sees the ship, and confirms that it is indeed Imperium Prime's ship. Manhunter then flies in to it, bursting through all the walls before making it to Prime himself. Manhunter then asks if prime remembers him, to which Prime replies that he doesn't. Manhunter then reminds him, revealing the Imperium took over his planet and killed every last Martian there was, it didn't matter if they where green or white, the Imperium killed them, but then Manhunter, then known as J'onn J'onzz, wiped out the Imperium, forcing Prime to retreet. Manhunter then tells Prime that he's going to finish the job, but Prime claims that he can change. Manhunter then stares at him, and replies that the sad part is Prime won't, and that he doesn't even want to. Manhunter then uses his laser vision once again and blasts Prime at full force, turning him in to nothing but ash.
Back with the others, an Imperium that Barry is fighting ends up blowing up on him, with the others following soon after. The ships then begin to crash, but Green Lantern uses all of his ring's power to catch every last ship and destroy them, before they crash. After this, Hal passes out from the strain of doing this.
Later, the team are given medals for saving the world. Clark asks them all if they're going to team up again in the future, with Bruce responding that they'll only team up for very big situations, like another invasion or a demon god attacking Earth. While thanking them, the man who gave them their medals asks them if their group has a name. Barry then says that he's been thinking of a name for them ever since they got here, with Clark and the others allowing him to say it. Barry then gets up on stage and says that their team is the Justice League.
End Credits Scene
A reporter is talking about the Justice League and how they saved the day from the Imperium. It is then paused and rewound to a scrolling video of the Justice League over and over again. It is then paused once more on Superman. A man's voice then asks a woman what her opinion on Superman is. She says she doesn't have one, with the man saying he thinks Superman is a ticking time bomb who could go off at any moment and take over the planet. She asks why that is, with the man saying that anyone that powerful will one day snap. He then says that he's going to take care of Superman before that happens before turning, revealing it to be Lex Luthor.
Manhunter mentions White Martians in the film. In the comics his protege, Miss Martian, is a White Martian herself.
During their conversation, Diana and Barry reference the events of their own films, with Barry mentioning how he fought the Rogues and Diana saying that she took down a "poison obsessed manic", meaning Doctor Poison.
When Hal is found he has a scar over his mouth, this was given to him by Sinestro during their fight, meaning this film takes place possibly only hours after Green Lantern.
When Barry first meets Bruce and Clark, he asks Bruce what he's getting out of this, with Bruce joking that he "just loves beating up people with white skin", referencing the Joker.
The end credit scene was a rejected Superman end credits scene with a few changes.