In 1975, eight-year-old Jean Grey inadvertently uses her telekinesis to cause a car accident that kills her mother and, apparently, her father. Shortly afterwards, Professor Charles Xavier takes her to Xavier's School for Gifted Youngsters, where he mentally blocks the accident from her memories and helps her in expanding her powerful psychic abilities.
In 1992, nine years after the worldwide devastation caused by En Sabah Nur, the X-Men are seen as heroes by the public. The President summons them for assistance during a crisis and respond to a distress signal from the space shuttle Endeavour, which is critically damaged by a solar flare-like energy during the STS-49 mission. While the X-Men save all of the astronauts, Jean is stranded and is struck by the energy which she absorbs into her body to save the X-Men's aircraft from destruction. Jean survives the event and her psychic powers are greatly amplified as a result. At the same time, the mental block placed by Xavier is destroyed and she accidentally unleashes her power on the mutants celebrating at Xavier's school. She then travels to her childhood hometown after discovering that her father is still alive. The X-Men attempt to take Jean home but she injures Peter Maximoff and accidentally kills Raven Darkhölme before flying away.
Jean travels to the mutant refugee island of Genosha to seek assistance from Erik Lehnsherr in controlling her powers, but is turned away by Erik after she engages in combat with U.S. military forces tasked with her arrest. Jean meets Vuk, the leader of a shape-shifting alien race known as the D'Bari, who explains to her that she has been possessed by a force of cosmic power which wiped out the D'Bari home planet years ago. The power had consumed all those it came across until it was drawn to Jean. Meanwhile, Hank McCoy, angered by Raven's death, allies with Erik and the mutant refugees in an attempt to kill Jean in New York City, in the hope of destroying the almighty universal force that now controls her.
Upon learning of Erik's plan, the X-Men try to stop him and his faction of mutants. As they battle, Erik manages to enter the building and confront Jean, but his power is neutralized by her tremendously amplified abilities, and he is then knocked out by her telekinetic attack. Xavier then enters the building with Nightcrawler. Jean attacks them until Xavier convinces her to read his memories – allowing her personality to resurface. Feeling remorseful, Jean offers to let Vuk take the force from her; however, it is revealed that doing so would kill Jean. Xavier and Scott are able to prevent Vuk from fully absorbing the force from Jean, though Jean loses consciousness from the ordeal. Troops sent by the U.S. government, who use stun weapons and power-disabling collars, attack and subdue both mutant factions, who are placed on a train headed towards a containment facility.
On the train, a remorseful Xavier admits to a resentful Hank that the latter was right in his earlier accusations of violating Jean's mind and lying to her. The train is attacked by Vuk and her D'Bari forces. When the soldiers are overpowered by the shape-shifters, the mutants are freed from their restraints to combat the threat. The mutants deal with most of the D'Bari attackers, but Vuk arrives and heads for Jean, defeating each mutant who attempts to stop her. Xavier confers with Jean within his mind, allowing Jean's personality to gain control of the force within her. After forgiving Xavier, Jean saves the mutants from Vuk's attacks and the ensuing train wreck before proceeding to easily disintegrate the remaining D'Bari when they attack her. Vuk once again attempts to drain Jean of the force, but Jean takes Vuk into outer space, retakes the power that Vuk had received earlier, and then kills her. Jean then disappears in a burst of energy in the form of a phoenix.
In the aftermath of the incident, the Xavier's school is renamed the "Jean Grey School for Gifted Youngsters", and Hank becomes their new dean with Xavier having retired after decades of fighting for mutant rights. While settling himself in Paris, Xavier is reunited with Erik and reluctantly agrees to play a game of chess with him. As they start playing, Jean appears in the sky revealing to be alive as she's slowly flying back to Earth.
- Sophie Turner as Jean Grey / Phoenix
- James McAvoy as Charles Xavier / Professor X
- Michael Fassbender as Erik Lehnsherr / Magneto
- Nicholas Hoult as Hank McCoy / Beast
- Tye Sheridan as Scott Summers / Cyclops
- Alexandra Shipp as Ororo Munroe / Storm
- Kodi Smit-McPhee as Kurt Wagner / Nightcrawler
- Evan Peters as Peter Maximoff / Quicksilver
- Jennifer Lawrence as Raven Darkholme / Mystique
- Jessica Chastain as Vuk and Margaret Smith
- Kota Eberhardt as Selene Gallio
- Andrew Stehlin as Ariki
- Ato Essandoh as Jones
- Scott Shepherd as John Grey
- Hannah Anderson as Elaine Grey
- Brian d'Arcy James as the President of the United States
- Lamar Johnson as Ben Hammill / Match
- Halston Sage as Alison Blaire / Dazzler
- Chris Claremont as a crowd member
The film received negative reviews from critics and audiences alik