Plot

A mysterious disease is spreading through the world with the media debating whether this is a doomsday scenario or a hoax. The disease quickly spreads through the animal population. At first, the disease has symptoms resembling that of rabies in the infected animals. The infection spreads through a bite and can jump through species.

A retired United Nations investigator Gerald "Gerry" Lane (Brad Pitt), his wife Karin (Mireille Enos) and their two daughters Constance (Sterling Jerins) and Rachel (Abigail Hargrove) are in heavy Philadelphia traffic when the city is attacked by zombies. Gerry watches as infected humans bite the healthy ones and turn them into zombies almost instantly.

As chaos spreads, Gerry's car has an accident and the family commandeers an abandoned RV and the Lanes escape to Newark, New Jersey. They try to gather groceries in a super market, but even that is attacked by zombies and the family takes refuge in a nearby apartment building, home to a couple with a young son, Tommy. Gerry receives a call from UN Deputy Secretary-General Thierry Umutoni, an old friend of Gerry's, who asks for Gerry's location and assures him that he is sending a helicopter to rescue him.

The next day, Gerald tries to convince Tommy's family to join his, as staying is not safe. However, Tommy's father refuses. The Lanes head to the roof of the apartment block. Not long after, zombies break into the apartment and turn everyone there but Tommy, who escapes. The Lanes are ambushed on the stairwell. Gerald holds them off so Karin and the girls can get to the roof. They are joined by Tommy, whom Gerald grabs and takes with him on the helicopter hovering overhead.

Thierry Umutoni (Fana Mokoena) had sent the helicopter that extracts the Lanes and Tommy to a U.S. Navy vessel in the Atlantic where scientists and military personnel are analyzing the worldwide outbreaks. Among them is virologist Dr. Andrew Fassbach (Elyes Gabel) who posits that the plague is a virus, and that development of a vaccine depends on finding the origin. The origin is suspected in a military facility in South Korea from where an email originated that mentioned the word "Zombie" for the first time while communicating the symptoms of the disease. Gerry reluctantly agrees to help Fassbach find the outbreak's source after it is made clear that he and his family will be removed from the ship if he does not.

Gerry and Fassbach fly to Camp Humphreys, a military base in South Korea, where they are attacked on arrival by zombies. Turning to re-enter the aircraft, Fassbach slips, falls and accidentally discharges his gun, killing himself. After being rescued by the base's surviving personnel, led by Captain Speke (James Badge Dale), Gerry learns that the infection was introduced to the base by its doctor. The doctor was infected in the field when he was treating a farmer who had zombie-like symptoms. The farmer was patient 0, & the doctor patient 1.

The Doctor was ultimately incinerated by a soldier with a lame leg who the infected ignored. A former CIA operative (David Morse), imprisoned at the base, tells Gerry to go to Jerusalem, where he says a safe zone has been maintained by the Israeli Mossad since before the outbreak's official acknowledgment. As Gerry and his team bike back to their aircraft, zombies attack, kill several soldiers and infect Captain Speke, who commits suicide to prevent himself from turning. Gerry and his C-130 pilot (Gregory Fitoussi) escape.

In Jerusalem, Gerry meets Mossad chief Jurgen Warmbrunn (Ludi Boeken), who explains that months earlier, the Mossad had intercepted a Indian military message claiming that Indian troops were fighting the Rakshasa, or "dead spirits". Israel had thereupon quarantined Jerusalem, erecting huge walls around it. Just as Jurgen shows Gerry that Israel is allowing survivors to take refuge in the city, loud celebratory singing from refugees prompts zombies to scale the walls and attack. Jurgen orders some Israeli soldiers to escort Gerry back to his plane. On the way, Gerry notices zombies ignoring an emaciated boy and an elderly man. Soon after, one of Gerry's escorts, a soldier who identifies herself only as "Segen" (Daniella Kertesz), is bitten in the hand, which Gerry quickly amputates to stop her turning. Gerry and Segen escape on a commercial airliner as Israel is overrun.

Gerry contacts Thierry, and the airliner is diverted to a World Health Organization (WHO) facility outside Cardiff, Wales. When a stowaway zombie attacks in mid-air, Gerry uses a grenade to blow the infected out of the aircraft, but this also causes them to crash. Gerry and Segen survive the crash, although Gerry is trapped in his seat and has sustained injuries. Segen comes to Gerry's aid, and together, they reach the Cardiff facility.

They proceed to the WHO facility, where Gerry loses consciousness. He awakens three days later and explains to the remaining WHO staff a theory he has, based on the people he has seen the zombies ignore. The infected do not bite the seriously injured or terminally ill, since they would be unsuitable hosts for viral reproduction.

He suggests that they test this by deliberately infecting somebody with a pathogen from the facility, but the pathogens are stored in a wing already overrun by zombies. Gerry, Segen and the lead WHO doctor go to get a pathogen. As they fight their way through, they are separated; Gerry continues to the pathogen vault while Segen and the doctor return to the main building. A zombie corners Gerry inside the vault, prompting him to inject himself with an unknown bacterium and open the vault, thereby testing his theory. The zombie ignores him, as do those he encounters while returning to the main building. Everybody rejoices at Gerry's success.

Gerry and his family are reunited in a safe zone at Freeport, Nova Scotia. A "vaccine", derived from deadly pathogens, is developed and issued to troops battling the infected, acting as a kind of camouflage. The vaccine also helps survivors to reach quarantine zones. Human offensives begin against the zombies, and hope is restored. "This isn't the end," Gerry comments, "Not even close. Our war has just begun."