An unidentified comet is found by Michigan State University's doctorate candidate in astronomy, Kate Dibiasky. Kate carries her discovery to her professor, Dr. Randall Mindy. Mindy tries to calculate the distance between the comet and planet Earth, where he discovers the comet will collide with Earth in about six months, and it is big enough to trigger a global extinction event. They soon inform NASA of the threat, and it confirms the results, Dibiasky and Mindy are accompanied by Dr. Teddy Oglethorpe, who is the head of the Planetary Defence Coordination Office when they present their findings to the White House.
They were asked to wait for a whole while the White House was busy celebrating birthday parties. Finally, the next day they were allowed in to meet the president and explain the impact of the comet hit. But President Janie Orlean and her son, Chief of Staff Jason Orlean, treat them with indifference. She even asks them to sit right and assess this situation. Dibiasky and Mindy are urged by Oglethorpe to leak the information to the media, and they do so on the well-liked morning talk show The Daily Rip.
Peter Isherwell, the founder and CEO of BASH Liif. He also receives information about the comet. Dibiasky explains to her boyfriend about the impact of the comet. The Daily Rip focuses on the show, which increases the TRP. Daily Rip was more interested in the breakups of celebrities and didn't take it seriously, but it was as fun when Dibiasky and Mindy explained about the comet hit and the extinction of the human species.
Dibiasky loses her cool and yells about the threat before leaving the scene as hosts Jack Bremmer and Brie Evantee approach the subject lightly. While Mindy gains popularity for his appearance on the show, Dibiasky is the target of offensive memes due to her actions while on television. The public pays little attention to actual news concerning the comet's threat, and Orlean's NASA Director Jocelyn Calder—a major contributor to the organization without any astronomical experience—denies the threat.
Dibisky calculates that the comet is going to hit the earth in precisely 6 months, 10 days, 2 hours, 11 minutes, and 41 seconds. Didbisky's boyfriend revealed their relationship to the media when she was trending funnily. To deflect negative attention from her sex scandal with her Supreme Court nominee Sheriff Conlon, Orlean ultimately confirms the threat and announces a nuclear weapons strike and comet diversion scheme.
Meanwhile, Mindy and Evantee develop a relationship. The expedition launched successfully, but Orlean unexpectedly ends it when she learns that the comet contains rare-earth materials valued at trillions of dollars. Peter is a billionaire CEO of BASH Cellular and another prominent supporter. The White House consents to deploy technologies suggested by BASH in an unreviewed plan to break up and retrieve the comet from the water to exploit it commercially. Orlean appoints Mindy as the National Science Advisor but ignores Dibiasky and Oglethorpe. Threatened, Dibiasky gave up trying to organize public resistance to the plan of Orlean's administration. Mindy becomes a proponent of the comet's business potential.
Dibisky took Orlean’s plan to the public directly, which resulted in people clamoring. Since then, there have been three schools of thought in the world: those who reject the comet's existence, those who dismiss alarmism and think that mining a destroyed comet will create jobs, and those who think the comet poses a serious threat. Mindy's wife finds his relationship with Evantee. Following their confrontation over his infidelity, Mindy's wife leaves for Michigan without him.
Dibiasky meets a teenage shoplifter named Yule at her retail job, and the two start dating when her parents push her out of the house when she returns to Illinois. Infuriating the billionaire, Mindy queries if Peter's technology can split the comet. Mindy finally loses it with the administration and goes on national television, attacking Orlean for downplaying the oncoming doom and raising doubts about humanity's lack of concern.
As the comet becomes visible from Earth, Mindy makes amends with Dibiasky after being cut off from the administration. A social media campaign led by Mindy, Dibiasky, and Oglethorpe encourages people to "Just Look Up" and calls on other nations to carry out comet interception operations. Concurrently, Orlean launched an anti-ad campaign, urging people to "don't look up". After Orlean and BASH denied Russia, India, and China access to the comet-mining agreement, these countries prepared a coordinated deflection mission, which ultimately resulted in the explosion of their spacecraft.
The comet grows in size, and Orlean's supporters begin to turn against her government. Mindy, Dibisky, her boyfriend, and Oglethorpe join Mindy's family to spend their last hours on Earth together. Everyone realizes that humanity is doomed after BASH's attempt to split the comet apart fails.
Unintentionally leaving Jason behind, Peter, Orlean, and other members of their elite circle board a sleeper starship intended to locate a planet similar to Earth. Mindy turns down Orlean's offer of two spots on the ship, preferring to spend one last night with his loved ones. The comet hits the coast of Chile as predicted, unleashing an extinction-level event and a global catastrophe. Every person inside Mindy's house dies as a result of the shockwave.
The 2,000 people who fled Earth before the comet's impact appear in a mid-credits sequence landing on a lush extraterrestrial planet 22,740 years later, breaking their state of suspended animation. As they step out of their spacecraft nude and take in the livable planet, Orlean is fatally attacked by a predator that resembles a bird and is part of a group that is encircling the newcomers to the planet.
Jason is seen to have survived the hit in a scene that takes place back on Earth after the credits have rolled. Declaring himself the "last man on Earth," he tapes himself and requests that everyone who watches "like and subscribe."
