The film opens with a parody of “2001: A Space Odyssey”, where it is shown, through the voice of the narrator (Helen Mirren) that the Barbie doll has been around since the dawn of girlhood. Random little girls are seen shattering their typical baby dolls in favor of the Barbie.
In the world of Barbie Land, there are multiple Barbies and multiple Kens (Ryan Gosling, Simu Liu, Kingsley Ben-Adir, Ncuti Gatwa, etc), as well as Allan (Michael Cera) and a pregnant doll named Midge (Emerald Fennell). There is a President Barbie (Issa Rae), Physicist Barbie (Emma Mackey), Doctor Barbie (Hari Nef), Writer Barbie (Alexandra Shipp), Diplomat Barbie (Nicola Coughlan), Journalist Barbie (Ritu Arya), and Mermaid Barbie (Dua Lipa), among others. The Kens live dependent on their relationships to their Barbies. The main Barbie (Margot Robbie) goes about her day enjoying her life in Barbie Land with her Ken (Ryan) and with her fellow Barbies. Ryan-Ken has a rivalry with Simu-Ken and they threaten to “beach off” one another. The Barbies and Kens all have a dance party to celebrate how great life in Barbie Land is, until Margot-Barbie comments on if anyone thinks about dying, completely killing the vibe.
Later on, Barbie starts to notice strange things going on in her life, including her heels now touching the ground and her skin having cellulite. She is told by the others ladies to visit Weird Barbie (Kate McKinnon), who has had her hair cut, her face drawn on, and she does splits. She explains to Barbie that there might be something going on in the real world with the girl who plays with her, and she must set out to find out what is going on with her. Barbie drives her way out of Barbie Land, accompanied by a stowaway Ken.
When Barbie and Ken make it to the real world (Venice Beach), they get into trouble after Barbie punches a guy who smacks her butt. After they get out of jail, Barbie goes off to try and find her owner. Barbie takes a moment to sit on a bench and see visions of a girl happily playing with her, until the girl ends up becoming less joyful, causing Barbie to shed tears. She then looks to her side and sees an old woman (Ann Roth) sitting next to her. Barbie tells her she is beautiful, and the woman says she knows.
Based on her visions, Barbie is directed to a middle school girl named Sasha (Arianna Greenblatt), who says she no longer plays with Barbies because they incorporate unrealistic beauty standards. Meanwhile, after Barbie and Ken split off, Ken ends up learning about the patriarchy, seeing it as something positive.
Barbie ends up at Mattel, the company that makes Barbies. The CEO (Will Ferrell) learns of her presence in the real world, which is overheard by an employee named Gloria (America Ferrera), who is also Sasha’s mother. Barbie ends up in the boardroom of employees, and the CEO tries to convince her to go back into a life-size box to fix everything. She nearly agrees before changing her mind and making a run for it. After Gloria picks up Sasha, she finds Barbie, who is being chased by the CEO and his subordinates. Barbie then learns that Gloria is responsible for her current existential crisis due to Sasha being more moody around her lately. Barbie guides Gloria and Sasha back to Barbie Land, while the guys from Mattel try to find a way to track her down.
When the three arrive in Barbie Land, they find that Ken has brought the patriarchy there, renaming the place “Kendom” and has now indoctrinated the other Kens into behaving more obnoxiously and more “bro” like, causing the rest of the Barbies to become more subservient to them. This extends to the real world where Ken’s change to Barbie’s dream house, a “Mojo Dojo Casa House”, starts selling well. While Barbie tries to appeal to Ken and get him to change his mind, he refuses because he now feels more valued than he did before going to the real world with her. Barbie becomes depressed and feels she is no longer perfect as she was made to be. Gloria and Sasha take her car and leave her when she tells them to go home. A commercial for “Depressed Barbie” plays before Weird Barbie comes to get her friend.
On their way out of Barbie Land, Gloria and Sasha are startled to find Allan has stowed away with them since he is already sick of the Kens having taken over. A group of Kens are building a wall (very poorly) to stop anyone from getting in or out of Barbie Land, and Allan begins to fight them all by himself. Sasha then decides they should go back to Barbie Land and help Barbie because Gloria cares about her, and Sasha expresses support for her mother’s ideas.
Gloria and Sasha return to find Barbie in Weird Barbie’s dream house, along with some discontinued Barbies and Kens. Gloria talks to Barbie, who is still depressed, and gives an impassioned speech about the standards women have to deal with in the real world. This helps snap Barbie out of her funk, as some of the other Barbies also come to their senses and devise a plan to get the Kens to change their minds.
Each Barbie tries to appeal to their Kens’ egos before jumping to other Kens to make them jealous and fight each other, culminating in a dance-off and Ken’s heartfelt “I’m Just Ken” ballad. Ken goes to Barbie and admits that he feels he is defined by his relationship to her, as it’s “Barbie AND Ken”, and not “just Ken”. Barbie apologizes for making him feel that way, but she also does not want to be known as just his girlfriend in Barbie Land. The Mattel guys arrive in Barbie Land, just as the spirit of Ruth Handler (Rhea Perlman), the creator of Barbie, appears to speak to her. Ruth tells Barbie that while humans might have an end, her story does not have to. She encourages her to choose her own destiny and holds her hands. Barbie closes her eyes and envisions other women and mothers before making her choice.
Later on, Barbie rejoins Gloria and Sasha in the real world, now going by the name Barbara Handler. The two drop her off at a building, where she tries to make an appointment to see a gynecologist.