X-Men Movie Timeline Explained

Original X-Men Timeline
1845: X-Men Origins: Wolverine (first section)
1962: X-Men: First Class
1979: X-Men Origins: Wolverine (second section)
2003: X-Men
2003: X2: X-Men United
2006: X-Men: The Last Stand
2013: The Wolverine
2023: X-Men: Days of Future Past

Relaunched X-Men Timeline
1845: X-Men Origins: Wolverine (first section)
1962: X-Men: First Class
1973: X-Men: Days of Future Past
1983: X-Men: Apocalypse
1990s: X-Men: Dark Phoenix
2029: Logan (possible alternate future)

Deadpool's Unclear Timeline
2016: Deadpool
2018: Deadpool 2


Original Timeline Explanation
8,000 BC: The ancient mutant Apocalypse rises to power in Egypt, but is betrayed by his followers and imprisoned. (X-Men: Apocalypse)
1832: James Howlett is born. (X-Men Origins: Wolverine)
1845: James' powers manifest, and he and Victor Creed abandon their family home to go on the run. They participate in many key conflicts over the next century, including the American Civil War and World War I. (X-Men Origins: Wolverine)
1930: Erik Lensherr is born.
1932: Charles Xavier is born.
1944: Erik Lensherr's powers begin to manifest at Auschwitz, and he becomes a test subject for Sebastian Shaw. (X-Men, X-Men: First Class)
1944: Charles Xavier meets Raven Darkholme. (X-Men: First Class)
1960s: Magneto tours the world seeking revenge on the Nazis responsible for the Holocaust. (X-Men: First Class)
1962: X-Men: Fist Class. Moira MacTaggert's investigations into the Hellfire Club lead her to discover the existence of mutants, and she approaches Charles Xavier for help. Xavier and Magneto form an alliance against Sebastian Shaw, with Xavier forming the first class of his X-Men. The X-Men confront the Hellfire Club at Cuba, and schism during the final confrontation, with Magneto creating his first Brotherhood of Mutants.
1963: Magneto is blamed for the assassination of President John F. Kennedy, although he insists on his innocence. (X-Men: Days of Future Past)
1965: Charles Xavier opens his School for Gifted Youngsters.
1970: Most of the staff and students of Xavier's School are drafted for the Vietnam War. Xavier sinks into depression. (X-Men: Days of Future Past)
1973: Mystique assassinates Bolivar Trask in Paris. The Sentinel project is unveiled, and immediately goes global. (X-Men: Days of Future Past)
1973: Logan quits Team X, which he presumably joined several years earlier. (X-Men Origins: Wolverine)
1975: Charles Xavier makes a closed-door appeal to United States politicians for mutant rights.
1977: Pietro Maximoff breaks world records in track and field events, but sparks a scandal when he is discovered to be a mutant.
1978: Colonel William Stryker sends his son to Xavier's School, but learns that Xavier is encouraging the use of his powers, and furiously withdraws him from the school. Stryker sends his own son to his Three Mile Island facility after the death of his wife. (X2)
1979: X-Men Origins: Wolverine. Sabretooth begins to hunt down and kill members of Stryker's old Team X, and murders Logan's lover. Logan is subjected to the Weapon X Project, his skeleton infused with Adamantium, but breaks lose and takes Trask's Three Mile Island facility down. He is shot in the head with an Adamantium bullet, and loses his memories. Charles Xavier recruits Three Mile Island escapees into his school. (X-Men Origins: Wolverine)
2001: The United States Government establish Guantanamo Bay Mutant Detention Center.
2003: X-Men. World leaders prepare to gather for a summit in New York discussing the mutant problem, and Magneto determines to use his technology to "mutate" them. In order to do so, he attempts to acquire Rogue in order to have her use her powers to duplicate his own, as Magneto believes powering this device will kill him. Magneto is stopped by the X-Men with the help of Wolverine, who has stumbled across Rogue and formed a bond with the child. (X-Men)
2003: X2: X-Men United. Colonel Stryker uses the mind-controlled Nightcrawler to launch an attack on the White House and justify the use of extreme measures to neutralize mutants. His agents raid Xavier's School, scattering the X-Men, and successfully capture Charles Xavier to use his powers to kill all mutants. The X-Men ally with Magneto and his surviving Brotherhood to defeat Stryker, although Jean Grey is believed killed during the confrontation. (X2: X-Men United)
2006: X-Men: The Last Stand. Worthington Industries develop a mutant cure, leading to a confrontation between the X-Men and the Brotherhood in San Francisco. A resurrected Jean Grey taps into her psychic powers and threatens all of humanity, but is killed by Wolverine.
2009: Trask Industries develops the inhibitor collar. They take possession of Xavier's School.
2012: Blink teleports 30 mutants out of a Trask mutant prison camp, the beginning of the resistance movement.
2013: The Wolverine. Wolverine travels to Japan in honor of an old debt, and is drawn into conflict with the Yakuza and the Silver Samurai. (The Wolverine)
2023: X-Men: Days of Future Past. The mutant rebels hit upon a desperate plan to rewrite history and erase this entire timeline. (X-Men: Days of Future Past)

The New X-Men Movie Timeline Made By Days Of Future Past
X-Men: Days of Future Past saw the X-Men successfully rewrite history by preventing the assassination of Bolivar Trask. They created a whole new timeline.
1962: X-Men: Fist Class. Moira MacTaggert's investigations into the Hellfire Club lead her to discover the existence of mutants, and she approaches Charles Xavier for help. Xavier and Magneto form an alliance against Sebastian Shaw, with Xavier forming the first class of his X-Men. The X-Men confront the Hellfire Club at Cuba, and schism during the final confrontation, with Magneto creating his first Brotherhood of Mutants.
1963: Magneto is blamed for the assassination of President John F. Kennedy, although he insists on his innocence. (X-Men: Days of Future Past)
1965: Charles Xavier opens his School for Gifted Youngsters.
1970: Most of the staff and students of Xavier's School are drafted for the Vietnam War. Xavier sinks into depression. (X-Men: Days of Future Past)
1973: X-Men: Days of Future Past. Wolverine's consciousness is transmitted from the future, and he allies with Charles Xavier and Magneto in order to prevent Mystique assassinating Bolivar Trask. Although the Sentinel program is still launched, it is disrupted by the X-Men and Mystique, and shut down.
1973: Charles Xavier reopens his School for Gifted Youngsters.
1976: Erik Lensherr meets Magda Gurzsky, and remarries.
1983: X-Men: Apocalypse. Magneto's family life ends in tragedy when his wife and children are killed. He is tricked into working with Apocalypse, who has been unwittingly awoken by Moira MacTaggert and is traveling the globe seeking new Horsemen. Weapon X soldiers take advantage of the crisis to capture the students of Xavier's School, but they escape with the help of Wolverine, whose skeleton has been implanted with Adamantium. Jean Grey ultimately defeats Apocalypse by unleashing her true power.
1992: X-Men: Dark Phoenix.
2023: An alternate-universe Wolverine awakens in this future timeline, experiencing a reality where old friends such as Cyclops and Jean Grey are still alive and Xavier's School is flourishing. (X-Men: Days of Future Past)

Logan's Future X-Men Movie Timeline
Logan takes place in a far future where almost all the X-Men are dead. It does have some connections to the core films - the post-credits scene of X-Men: Apocalypse explained where Essex Corps. obtained the genetic material they used to create X-23 - but dialogue links it into the original timeline. It feels like more of a parallel reality all of its own, and thus is handled separately here.
2014: The birth of the last generation of natural mutants. This was believed to be a natural phenomenon, but in reality it was because Alkali had introduced mutant-suppressing chemicals into common foodstuffs.
2018: The X-23 project creates Laura Kinney, a female clone of Wolverine.
2028: Charles Xavier suffers a massive psychic seizure, injuring over 600 people in Westchester and killing his X-Men. Wolverine takes Xavier to live an isolated life in Mexico.
2029: Logan. Some of the X-23 children escape Transigen, and attempt to travel to sanctuary in Canada. Laura tracks down Logan and Xavier, and they help her and the other mutant kids escape Transigen's hunters. Both Xavier and Logan are killed accomplishing their goal.

Deadpool's Alternate X-Men Movie Timeline
The Deadpool movies take place in some version of the X-Men movie timeline but, fitting of their fourth-wall breaking anti-hero, they don't really slot alongside the other movies in any obvious way (especially considering Deadpool 2's cameo from the Dark Phoenix core cast and mind-melting time travel). For the sake of coherence, we're treating them as a whole alternate timeline.
2010: The Weapon X Project is reactivated by the US Government, and they begin to create living weapons to sell to the highest bidder. The first wave include Ajax and Angel Dust.
2014: Mercenary Wade Wilson meets Vanessa Carlyle, and the two begin a relationship.
2015: Wade Wilson is diagnosed with cancer, and agrees to be subjected to an experimental process that he believes will cure him. The experience leaves Deadpool badly disfigured; furious, he seeks revenge on Ajax.
2016: Deadpool, Colossus, and Negasonic Teenage Warhead successfully defeat Ajax and his allies. Wade becomes a mercenary and assassin for hire.
2018: Vanessa is killed by gangsters, and a heartbroken Deadpool initially tries to kill himself. He builds a friendship with Firefist, a young mutant who was being abused at the Essex House for Mutant Rehabilitation, and both are imprisoned in the Ice Box. They soon cross paths with the time traveler Cable, who originates from a timeline in which Firefist became a dangerous villain.
2068: In an averted timeline, Cable's wife and daughter are killed by the mutant Firefist. He travels back to rewrite history.

Problems With The X-Men Movie Timeline
Viewed from a distance, the X-Men films' continuity just about works; but the devil, as they say, is in the details. X-Men: First Class is intended to be part of both timelines, and yet it contradicts the original X-Men trilogy in several details, including the origin of Cerebro, Xavier's historic relationship with Mystique, and his early experience of Magneto's psychic-blocking helmet. X-Men: Days of Future Past's future sections sit uncomfortably with X-Men: The Last Stand and The Wolverine, most notably with Xavier's being back in what appears to be his original body and Wolverine regaining his Adamantium claws.

Meanwhile, some of the timeline changes make absolutely no sense at all. The Cyclops of X-Men Origins: Wolverine was clearly born before the timeline changed, and yet the character in the rewritten timeline is a completely different age. Angel's age is likewise inexplicable; two different versions appear in 1983's X-Men: Apocalypse and 2006's X-Men: The Last Stand. In truth, the explanation is a simple one from an out-of-universe perspective; Fox used the reboot to start again, and haven't been particularly interested in maintaining any sense of continuity between the original X-Men trilogy and the relaunch.