The movie begins by highlighting a fascinating history: over three centuries ago, the first metahumans were discovered, marking the dawn of a new era filled with gods and monsters. The story then shifts to a real-world timeline, 30 years prior, when Jonathan and Martha Kent (Pruitt Taylor Vince and Neva Howell) discovered a baby named Kal-El on their farm. They adopted him, raising him as Clark, who would later become Superman (David Corenswet). As Clark matures, he discovers his extraordinary powers, becoming the most powerful metahuman and a celebrated superhero protecting Metropolis.
The plot becomes more intense three weeks before the current timeline, when Superman intervenes in Boravia, preventing soldiers from invading the neighboring country of Jarhanpur. His actions, however, stir controversy internationally, especially among political leaders. Soon after, a mysterious new villain appears—known as the "Hammer of Boravia"—who swiftly overpowers Superman in combat. The villain is revealed to be Ultraman, a clone of Superman created by the nefarious billionaire Lex Luthor (Nicholas Hoult), who views Superman as a threat to human dominance.
Following the battle, Superman lands in the Arctic, where he calls out to his loyal superdog, Krypto. With Krypto’s help, Superman makes his way to the Fortress of Solitude, where a team of AI robots (Alan Tudyk, Michael Rooker, and Pom Klementieff) care for him. They place Superman in a healing chamber, showing him a heartfelt video message from his lost parents, Jor-El (Bradley Cooper) and Lara (Angela Sarafyan), revealing vital truths about his origins.
Rejuvenated, Superman returns to Metropolis to confront Ultraman and Luthor’s growing schemes. Luthor, who despises Superman for making ordinary humans feel insignificant, collaborates with the Justice Gang—a team of other metahumans including Green Lantern (Nathan Fillion), Mr. Terrific (Edi Gathegi), and Hawkgirl (Isabela Merced). Their mission is to contain the chaos caused by Luthor’s experiments and the giant monster he unleashes upon the city. Superman tries to negotiate peace but is dismayed when Mr. Terrific prematurely destroys the monster from the inside, leading to mixed reactions among the citizens.
Amidst the chaos, shocking revelations surface: a secret message from Jor-El and Lara explicitly states that Superman was sent to Earth to conquer it. This revelation ignites public outrage, turning the hero into a public enemy. Clark Kent ([David Corenswet]) struggles with this betrayal, especially as media figures such as Peacemaker cast blame and skepticism on him. Lois Lane ([Rachel Brosnahan]) confronts Clark at his apartment, where he finally admits his identity as Superman. She urges him to stay out of foreign conflicts, leading to a temporary breakup as Clark wrestles with his role and identity.
Meanwhile, Luthor intensifies his plans. He journeys to Antarctica with Ultraman and Angela Spica (The Engineer) ([Mara Gabriele de Faria]), who has been infused with nanites that allow her to produce any weapon. Luthor's forces break into the Fortress, abduct Krypto, and uncover a hidden message from Jor-El and Lara, which Clark was previously unaware of. Luthor's minions unleash a kaiju — a monstrous creature intended to terrorize Metropolis. Superman attempts to quell the chaos peacefully but faces fierce opposition.
The Justice Gang, led by Guy Gardner/Green Lantern ([Nathan Fillion]), joins Superman in fighting the monster. Their efforts are thwarted when Mr. Terrific opts to destroy the creature from within, causing alarm. Luthor then broadcasts a video revealing his plan to manipulate global conflicts and orchestrate Superman’s downfall. This drives Superman into despair, especially after he learns his parents’ true intentions.
Luthor’s machinations escalate as he captures Superman and imprisons him within a pocket dimension—a space Luthor has designed as a personal prison. Luthor also threatens Malik Ali, a civilian who aided Superman, forcing him to create kryptonite, which weakens the hero. During this ordeal, Superman’s ally Eve Teschmacher (Sara Sampaio) grows disillusioned with Luthor’s cruelty and secretly works to aid Lois and Jimmy Olsen (Skyler Gisondo). Lois learns of Eve's covert efforts and races to rescue Clark, enlisting help from Mr. Terrific.
Meanwhile, Superman and his allies manage a daring escape from the dimensional prison, with Lois and Terrific risking everything to free him, Krypto, and the others. Clark is taken back to Smallville, where his parents’ memory and guidance inspire him anew. His dad, Jonathan Kent, reminds him that "the choices you make make you the hero you are", reinforcing Clark’s resolve.
In a final showdown, Luthor attempts to unleash chaos by opening the dimensional rift again, leading to a final fierce battle. Superman confronts Ultraman, revealing him to be a clone, and with the help of the Justice Gang, manages to terminate the clone and close the rift. Clark’s heartfelt speech about his humanity and dedication to protecting Earth resonates with the public, restoring his image as a true hero.
The movie concludes with Clark embracing his role fully, sharing a passionate kiss with Lois while floating in the air, symbolizing hope and new beginnings. Jimmy and Eve also start a relationship after she is freed. Superman then returns to the Fortress of Solitude, where he reconnects with his robotic friends and is visited by his cousin, Supergirl (Milly Alcock), who comes to take Krypto home.
In the closing scenes, Superman is shown overlooking Earth from the moon, cuddling Krypto, while post-credits scenes hint at ongoing adventures and challenges, including Superman and Mr. Terrific discussing a slightly crooked building, emphasizing that even superheroes deal with imperfect situations but continue to stand strong for justice and peace.
