Light years from Earth, 26 years after being abducted, Peter Quill finds himself the prime target of a manhunt after discovering an orb wanted by Ronan the Accuser.
In 1988, following his mother's death, a young Peter Quill is abducted from Earth by the Ravagers, a group of space pirates led by Yondu Udonta. Twenty-six years later on the planet Morag, Quill steals a sphere-like artifact only to be intercepted by Korath the Pursuer, a subordinate to the fanatical Kree Ronan the Accuser. Although Quill escapes with the artifact, Yondu discovers his theft and issues a bounty for his capture while Ronan sends the assassin Gamora after the orb, which Ronan seeks to give to the titan Thanos in exchange for destroying the Xandarians.
When Quill attempts to sell the orb on the Nova Corps homeworld - Xandar, Gamora ambushes him and steals it. A fight ensues, drawing in a pair of bounty hunters; the genetically-engineered raccoon Rocket, and the tree-like humanoid Groot. The Nova Corps arrives and arrests the group, imprisoning them in The Kyln. A powerful inmate, Drax the Destroyer, attempts to kill Gamora due to her association with Ronan, who killed his family. Quill dissuades him by saying that Gamora can bring Ronan to him. Gamora reveals that she has betrayed Ronan, unwilling to let him use the orb's power to destroy entire planets such as Xandar. Learning that Gamora has a buyer for The Orb, Rocket, Quill, Groot, and Gamora work together to escape the Kyln.
Elsewhere, Ronan meets with Thanos to discuss his daughter Gamora's betrayal and the loss of the orb, during which Ronan kills Thanos's servant, The Other.
Now accompanied by Drax, Quill's group escapes the Kyln in his ship—the Milano—and flee to Knowhere, a remote criminal outpost in space built in the giant severed-head of a celestial. Drunk and seeking vengeance, Drax secretly sends a message to Ronan revealing the group's location, while the rest of them meet with Gamora's contact, Taneleer Tivan. Tivan opens the orb, revealing an Infinity Stone, an item of immeasurable power that destroys all but the most powerful beings who wield it. Suddenly, Tivan's tormented assistant, Carina, grabs the stone, triggering an explosion that engulfs his collection and destroys Carina.
Ronan arrives and easily defeats Drax, while the others flee by ship, pursued by Ronan's followers and Gamora's sister Nebula. Nebula destroys Gamora's ship, leaving her floating in space, and Ronan's forces leave Knowhere with the sphere. Quill contacts Yondu before following Gamora into space, giving her his helmet to survive; Yondu arrives and retrieves the pair. Rocket, Drax, and Groot threaten to attack Yondu's ship to rescue them, but Quill negotiates a truce by convincing Yondu that they can recover the orb. The group agrees that facing Ronan means certain death, but that they must stop him from using the Infinity Stone to destroy the galaxy. On Ronan's ship, the Dark Aster, Ronan embeds the stone in his warhammer, taking its power for himself. He contacts Thanos, threatening that after the destruction of Xandar, he will kill Thanos; hateful of her adopted father, Nebula allies with Ronan.
On Xandar, the Dark Aster is confronted by Yondu's fleet, the Nova Corps, and Quill's group, which breaches the Dark Aster. Ronan uses his upgraded warhammer to destroy the Nova Corps fleet. Drax kills Korath, and Gamora defeats Nebula (who escapes) and unlocks Ronan's chambers, but the group finds themselves outmatched by his power until Rocket flies the Milano through the Dark Aster and crashes into Ronan. The damaged Dark Aster crash lands on Xandar, with Groot sacrificing himself to shield the group. Ronan emerges from the wreck and prepares to destroy Xandar, but Quill distracts him by dancing, allowing Drax to destroy Ronan's warhammer. Quill grabs the freed stone, and with Gamora, Drax, and Rocket sharing its burden, they use it to destroy Ronan.
In the aftermath, Quill tricks Yondu into taking a container supposedly containing the recovered stone, then gives the real stone to the Novas. As The Ravagers leave Xandar, they remark that it turned out well that they did not deliver Quill to his father following his abduction. Quill's group, now known as the Guardians of the Galaxy, have their criminal records expunged, and Quill learns that he is only half-human, his father being part of an ancient, unknown species. Quill finally opens the last present he received from his mother, which contains a mix tape of her favorite songs. The Guardians leave in the rebuilt Milano accompanied by a twig recovered from Groot, which is already beginning to grow and regenerate. In the post-credits scene, Tivan sits in his destroyed archive, where he is licked by Cosmo the Space Dog, and mocked by one of his collections, Howard the Duck.
- Chris Pratt - Peter Quill
- Dave Bautista - Drax
- Vin Diesel - Groot
- Bradley Cooper - Rocket
- Zoe Saldana - Gamora
- Benicio del Toro - Taneleer Tivan
- Ophelia Lovibond - Carina
- Lee Pace - Ronan the Accuser
- Djimon Hounsou - Korath the Pursuer
- Josh Brolin - Thanos
- Glenn Close - Irani Rael
- John C. Reilly - Rhomann Dey
- Karen Gillan - Nebula