Sara Matthews (Minka Kelly) is starting her freshman year of college. She meets Tracy (Aly Michalka), Stephen (Cam Gigandet) – her love interest, and Rebecca (Leighton Meester) – her college roommate. The girls begin to bond and Rebecca learns that Sara had an older sister, Emily, who died when Sara was nine, and an ex-boyfriend, Jason (Matt Lanter), who keeps calling her in attempts to reconcile. As time goes on, Rebecca's obsession with Sara grows, which causes her to drive away anyone who could come between them.
Rebecca attacks Tracy in the shower, pinning her down and ripping out her belly-button ring, and says that she is a bad influence on Sara and threatens to kill Tracy unless she stays away from Sara. Tracy moves to another dorm, fearful of Rebecca. An old friend of Sara's named Irene (Danneel Harris), who is a lesbian, invites Sara to move in with her when Sara's cat Cuddles is discovered. Rebecca then kills Cuddles by putting her in the dryer. She then lies to Sara that the cat ran away. Rebecca then inflicts injuries upon herself and says she was assaulted by a thug. Sara feels bad for her and decides to spend the Thanksgiving with Rebecca. When Sara's philandering fashion design professor, Roberts (Billy Zane), kisses her, Rebecca plans to get the professor out of the picture by seducing him while recording their dialogue on a tape recorder to make it sound like he was trying to rape her.
During her stay, Sara overhears a conversation between Rebecca and her father (Tomas Arana), hinting Rebecca has had trouble making friends in the past. Rebecca's mother (Frances Fisher) mentions that Rebecca is supposed to be taking medication. She and Stephen later find a bottle of Zyprexa pills, used to treat schizophrenia and bipolar disorder. But the bottle is full, implying that Rebecca hasn't been taking the pills. Sara, worried about what would happen, decides to move in with Irene. Irene goes to a club where she sees Rebecca. They make out in the club's bathroom and Irene, not knowing that Rebecca is Sara's roommate, takes Rebecca back to her place. The following morning, Sara goes to Irene's apartment but she's not there.
Rebecca gets Sara's sister's name tattooed in the same place on her breast as Sara, saying that Sara can now think of Rebecca as her sister. A shocked Sara realizes that Rebecca is obsessed with her and packs all her things, except her sister's necklace, which she can't find (being later revealed that the necklace had been stolen from her by Rebecca). Jason arrives at Sara's dorm and slips a note under her door, saying that he wants to see her. Rebecca reads the note, impersonates Sara with her sister's necklace and tattoo, and dyes her hair to look like Sara. She then goes to Jason's hotel room and stabs him to death.
Later, Sara gets a text from Irene, saying she needs her right away. Sara informs Stephen she will be at Irene's place. When she gets there, she finds Irene gagged with her arms spread and each of her wrists handcuffed to each end of her bedpost while being held hostage by Rebecca with a revolver. Rebecca reveals that she was responsible for what happened to Tracy, Cuddles, Professor Roberts, and Jason and that she did it all to win Sara's friendship. Rebecca wants to kill Irene in order to finally have Sara all to herself. Stephen arrives just in time to help stop Rebecca from pulling the trigger on Irene. Sara reaches for the revolver to shoot Rebecca, however, the cartridge is empty. Enraged, Rebecca attacks Sara and tries to strangle her, but Sara stabs Rebecca in the back with a boxcutter, killing her.
Sara moves back into her dorm and moves the extra bed out of her room with the help of her boyfriend Stephen, proclaiming that she does not want a roommate for a while.
Sonny Mallhi first thought of shooting the film in New York City but it was eventually shot on location at the University of Southern California in Los Angeles and at Loyola Marymount University. Leighton Meester was originally set to play Sara but was replaced by Minka Kelly and Leighton played Rebecca. Billy Zane and Frances Fisher had both starred together in Titanic thirteen years earlier, though in this film they shared no scenes.
The film was originally planned to be released on September 17, 2010, but was moved to February 4, 2011. The trailer was shown with Devil and Burlesque.
Opening in 2,534 theaters, the film grossed $15.6 million its opening weekend to take first place at the box office. Its distributor estimated that females under the age of 21 accounted for two-thirds of its audience. At the end of its run in 2011 the film grossed $37,300,107 in the United States and Canada and $3,192,652 in other countries for a worldwide total of $40,492,759.
The Roommate was released on Blu-ray Disc, DVD, and digital download in North America on May 17, 2011.
The Roommate was given negative reviews by critics. As of May 30, 2014, the film held a 4% rating on Rotten Tomatoes, based on 84 reviews with a consensus of it being "Devoid of chills, thrills, or even cheap titillation, The Roommate isn't even bad enough to be good." CinemaScore polls indicated a "B−" rating from audiences.
Keith Staskiewicz of Entertainment Weekly gave the film a D, saying it "is really just a far-below-par thriller that desperately wishes it were a different movie – a longing it shares with the audience," but praises Meester for bringing "the slightest trace of something fascinating to her role. When she smiles, it's perfectly located between a sweet display of affection and a snarling warning." Peter Travers of Rolling Stone gave it a half star, stating that "The Roommate – the umpteenth uncredited remake of 1992's Single White Female – sucks bad, real bad" and that "Danish director Christian E. Christiansen has no flair for suspense". Meester's performance garnered praise from other top critics, including the Los Angeles Times, which states: "Here her performance often has the feeling of a sports car in neutral. When she punches it for quick changes of tone from manic to wounded or around the bend, she shows how much more she is capable of."
Some of the promotional posters and displays for the film used the Christy Administration Building from Southwestern College in Winfield, Kansas as its backdrop. The college administration voiced concern that permission to use the photograph of the building was not properly obtained and investigated the legality of its use.
Primary concerns hinged that the image of the college (particularly the image of the building) could be damaged, while other concerns were that the college's primary iconic image was being used for promotion of an unrelated business venture.
After initial success became realized when the film earned $15.6 million in receipts to top the box office during its debut weekend in the United States, concerns continued. By that time, the image of the building had been replaced on the film's official website and on subsequent promotional material. The photo of the building reportedly was licensed from iStockPhoto based in Calgary, Alberta. As of February 8, 2011, no lawsuits had been filed but discussions had taken place.
Students at the school reported "mixed feelings" about the topic – some believed that it may have been helpful for the college and others reported that they saw how it could have been harmful to the school's image.