The film received a rating of PG-13 for violent content and images, and was released on February 26, 2008. It is the second film in the series of DC Universe Animated Original Movies released by Warner Premiere and Warner Bros. Animation; the first release was Superman: Doomsday and the next film in the series is Batman: Gotham Knight. The film had its broadcast premiere on October 18, 2008 on Cartoon Network.
An unknown entity has decided to eradicate mankind due to its capacity of violence.
At the end of the Korean War, United States Air Force pilot Hal Jordan and his wingman, Kyle "Ace" Morgan, are attacked by enemy pilots but survive. In Gotham, J'onn J'onzz—the last survivor of the Green Martian race— is teleported to Earth; unable to return, J'onn disguises himself. In Las Vegas, Iris West is on the telephone with her fiancé Barry Allen—known as Flash— at a casino when Captain Cold arrives to commit robbery; he races from Central City to confront Cold. Flash finds the six bombs hidden by Cold and captures him, before Cold is possessed by an entity.
After two years, J'onn (as John Jones) is a detective with the Gotham City Police Department. A doomsday cult that worships "The Centre" has kidnapped a child for a sacrificial ritual; J'onn and his partner Slam Bradley join Batman in battling the cult, but a fire renders J'onn powerless. The cult leader is possessed by the entity, who identifies itself as "The Centre", and warns of impending judgement. Hal trains under Col. Rick Flag at Ferris Aircraft for a U.S. government project, as explained by Carol Ferris, to build a spacecraft for travel to Mars. Special agent King Faraday oversees the project.
Batman suggests to J'onn that they work together in investigating the Centre-worshiping cult. The Flash defeats a robotic duplicate of Gorilla Grodd; after being targeted by the government, he announces his retirement. J'onn interrogates former Ferris employee Harry Leiter, who tells them about the launch to Mars and when Faraday arrives, J'onn briefly glimpses into his mind to learn the truth. Seeing the contemptuous response to the Flash's announcement, J'onn gives his research to Batman and plans to hide on the rocket. J'onn and Faraday fight on the launchpad; the rocket is damaged and malfunctions after leaving Earth's atmosphere. Hal wants to attempt a landing but Flag reveals weapons of mass destruction are on board, intended to destroy any life on Mars. Hal is ejected from the cockpit and saved by Superman; Flag detonates the rocket as J'onn is held prisoner.
On Paradise Island, Wonder Woman trains with Mala before being attacked by The Centre. Abin Sur gives his ring to Hal and tells him of The Centre, which is described as a monstrous creature that seeks the destruction of humans. Superman and Batman review J'onn's research as Lois Lane reports that a giant pterodactyl is attacking Cape Canaveral. Wonder Woman's invisible jet crashes and she warns that The Centre is coming. J'onn decides to help save Earth after his hope for humanity is renewed. The Centre, a massive flying island with an army of mutant dinosaurs to guard it, begins attacking Florida. The Flash, Green Arrow, Adam Strange, the Challengers of the Unknown, and the Blackhawks work with the soldiers on the base; Superman reconnoiters The Centre but is defeated. Moved by his efforts, the heroes plan to use Ray Palmer's reduction ray to destabilize the island along with a frontal assault and bombing mission.
The aerial assault is nearly outmatched and a herd of dinosaurs ambush Faraday's ground forces. The Centre's psychic force briefly overwhelms J'onn. Faraday is captured by a dinosaur and both perish after Faraday sets off hand grenades. Hal and Ace shoot their way into The Centre's core but a hallucinogenic attack disorients them; a thick red fluid jams their weapons and almost suffocates them. Hal's ring relays instructions from the Guardians of the Universe on its use. Ace detonates his payload before Hal rescues him. The Flash races across the ocean, leaps onto The Centre's surface and covers it on foot. The Centre begins to shrink; Hal envelops the island in green energy, towing it into space where it explodes. As the team celebrates their victory a glowing light emerges from the water and Aquaman emerges from a submarine carrying Superman.
The world celebrates The Centre's defeat with a ceremony. The film ends with a montage of various heroes and villains, including the birth of the Justice League set to the titular John F. Kennedy speech.
Like Superman: Doomsday, Justice League: The New Frontier had a soundtrack released by La-La Land Records on March 18, 2008. The music was composed by Kevin Manthei, the track listing is as follows.
Justice League: The New Frontier received mostly positive reviews. Screener copies were sent to website reviewers a month before the DVD's official release. Most of the reviews were positive and geared up the film's release even more. Newsarama reviewed the film, saying that it was "one of the best things to ever come out of [Bruce] Timm's stable", and said that the acting was exceptional. The World's Finest, a fansite dealing with DC Animations, said that it was "the first animated feature in a long time that I've felt completely satisfied while walking away from." A reviewer from Ain't It Cool News said that it was "my favorite film of 2008", and that it was "everything I had hoped for." Mainstream websites made similar comments; IGN gave the film and DVD a total score of 8.0, ENI said it was enjoyable, and DVDTalk.com said it was "recommended". The New Frontier was nominated for an Emmy in the category of Outstanding Animated Program (for Programming One Hour Or More) in 2008.
Justice League: The New Frontier is available in single and two-disc editions. The cover of the single disc includes the panoramic image from the film, while the two-disc, HD DVD and Blu-ray editions have an image of Superman, Batman and Wonder Woman above the title logo with other characters below it. Best Buy had an exclusive deal which included a Green Lantern action figure from DC Direct with the DVD package. Wal-Mart had an exclusive single DVD package with "The New Frontier Green Lantern" CD-ROM Comic Book inside. The single, two-disc and Blu-ray editions were released on February 26, 2008, with the HD DVD edition released on March 18, 2008.
The special features include a documentary on the forty-seven year history of the Justice League, commentaries, a documentary on the early mythological villain archetypes in the Justice League stories, a featurette on the themes, elements from the comic to film versions of New Frontier, three episodes of Justice League Unlimited and a 10-minute preview of the animated film; Batman: Gotham Knight. Variety said that pre-orders for The New Frontier were greater than expected at that time.