While venturing into the depths of space to seek out new habitable planets, a probe from the Life Foundation—an ambitious bio-engineering firm—stumbles upon a comet teeming with symbiotic lifeforms. As they retrieve four samples and bring them back to Earth, an accident results in one of the samples escaping, leading to a catastrophic ship crash in Malaysia. Although search teams fail to locate the escaped sample, one astronaut miraculously survives the wreckage.
Once the astronaut is taken to an ambulance for emergency care, the dormant Symbiote seizes control of his body, ultimately causing the destruction of the ambulance. The Symbiote, now inhabiting the form of a nurse, acquires the astonishing ability to heal human bodies and sets its sights on the Life Foundation's insignia, directing its movements toward the corporation.
Driven by insatiable hunger, the Symbiote shifts from one body to another, relentlessly pursuing its target. Back at the Life Foundation's research facility in San Francisco, CEO Carlton Drake—a brilliant inventor deeply involved in symbiotic experiments—discovers that these lifeforms cannot thrive without breathable hosts, often resulting in fatal rejections unless the organism is a suitable match.
Enter investigative journalist Eddie Brock, who uncovers troubling information about Drake’s human trials through a classified document linked to his fiancée Anne Weying, an attorney preparing a defense for Life Foundation against lawsuits. Confronting Drake on his practices, Brock accuses him of leveraging vulnerable populations as test subjects in exchange for monetary compensation, which tragically leads to fatalities among many.
This bold confrontation costs both Brock and Weying their jobs, culminating in a painful breakup. Among the many who support Brock is Mrs. Chen, a convenience store owner played by Peggy Lu. When Mrs. Chen's store is robbed and Brock, paralyzed by fear, fails to intervene, her support for him remains unwavering.
Fast forward six months, and Drake is close to successfully bonding the Symbiotes with human hosts. Dora Skirth, a scientist working under Drake, is concerned about the ethics of his methods and confides in Brock the dangers posed to test subjects. She reveals that alien lifeforms were recovered from the probe and expresses her desire to expose Drake due to her growing fears for her safety.
With Skirth’s guidance, Brock breaks into the facility to gather evidence, only to find that a homeless woman named Maria has become one of Drake's unwilling test subjects. In a desperate act to save Maria, Brock inadvertently becomes the new host for the Symbiote when it transfers from her, leading to her demise.
As he escapes, Brock experiences a shift in his physical abilities—displaying incredible strength, speed, and agility, yet succumbing to strange cravings and bizarre behavior, prompting him to seek assistance from Weying. Her new partner, Dr. Dan Lewis, examines him and discovers the presence of the Symbiote.
Meanwhile, Drake retaliates against Skirth’s betrayal by exposing her to another captive Symbiote, which ultimately dies, leaving Brock’s Symbiote as the last known survivor. When mercenaries are dispatched to capture Brock, the Symbiote manifests as a formidable creature, defending Brock against threats and providing him with extraordinary abilities.
Finding refuge outside the city, the Symbiote communicates its identity as Venom and reveals a dire invasion plan: the comet is part of a force aiming to conquer planets by consuming their inhabitants. Venom proposes an alliance, and Brock begins to appreciate the superhuman powers granted by this bond.
Determined to expose Drake's heinous acts, Brock returns to his former workplace, but is intercepted by authorities and transforms once more to evade capture. Witnessing this, Weying brings him back to Lewis, where they discover that the bond with Venom is jeopardizing Brock’s health—as the Symbiote causes significant organ damage.
Identifying the Symbiote's vulnerabilities—sound frequencies and fire—Weying uses an MRI to create a temporary rift, allowing Brock to separate from Venom. However, Brock is soon imprisoned by Drake's forces. At the same time, the fourth Symbiote, Riot, maneuvers from Malaysia to San Francisco, eventually fusing with Drake, who anticipates launching an expedition to gather the other Symbiotes from Earth.
Reluctantly, Weying decides to ally with Venom to rescue Brock. When the duo reunites, Venom reveals a newfound motivation to protect Earth, influenced by their shared experiences. Together with Weying, they intervene just as Riot and Drake attempt to launch a space probe, which ultimately explodes, resulting in the demise of both adversaries.
Though Weying assumes that Brock has been severed from Venom following this explosion, the bond remains intact, and they embrace their roles as vigilantes, navigating the criminal underbelly of the city. Brock reinvigorates his career in journalism, culminating in a gripping mid-credits scene where he’s invited to interview imprisoned serial killer Cletus Kasady, who ominously taunts about the "carnage" that’s yet to come.
