In the nightclub scene of the 1970s New York City, a multiracial young girl, Billie, born to a Caucasian father and an African-American mother, is taken away from her alcoholic, lounge singer mother after she is deemed irresponsible to raise her and Billie's estranged father wants nothing to do with either one of them. Billie spends the rest of her teenage years in an orphanage.
Years later (in 1983), the 19-year-old Billie (Marah Carrey) works as a nightclub dancer along with her foster-care friends Louise and Roxanne. They meet Timothy Walker (Terrence Howard), a record promoter who offers the three of them a contract as backup singers/dancers to the singer Sylk. Initially, Billie refuses, hoping to achieve stardom on her own terms. After pestering from her friends, Billie relents and the three are contracted. They record the hit single, "All My Life" but Sylk's vocal is sub-standard. To maximize sales based on the sex appeal of Sylk, Timothy asks Billie to sing while Sylk lip-syncs.
Later at a nightclub, Billie sings Sylk's song which gets her noticed by the club DJ, Julian "Dice" Black, during the public debut of "All My Life". Dice, knowing that Sylk is an indifferent singer, is shocked by the arrangement, but goes backstage to congratulate Billie for singing the song. Sylk insults her backup singers in front of a photographer and Billie, not wanting to take the verbal abuse, exposes Sylk by singing "All My Life" a cappella in front of Dice. Impressed, he wishes to produce her, but Billie turns him down, thinking that he wants to exploit her talent. When Billie relents after Dice pesters her, she raises concerns about her contract with Timothy. Dice threatens to not play any more artists from Timothy in his nightclub unless Timothy surrenders Billie and her friends' contacts. Timothy eventually agrees on the provision that Dice pays him $100,000.
Billie and Dice start working on songs: the first being the hit underground single, "Didn't Mean to Turn You On". Dice advises Billie to play off record companies to secure a bigger deal. Ultimately they sign with Guy Richardson of a major record label. With success in their hands, Dice asks Billie to dinner. Later, he asks her up to his apartment and they sleep together.
Billie's first major single, "Loverboy" is a success. The music video originally features Billie, Louise, and Roxanne. However, the director, dissatisfied with the results, orders Billie to wear more revealing clothing and replaces Louise and Roxanne with professional semi-nude male dancers. When the male dancers are then ordered to dance closely to Billie, this frightens her. Dice intervenes on her behalf, and they leave the set before the music video can be finished.
Dice is denied permission to produce songs on Billie's debut, including "Reflections", which Billie wrote about her mother. Billie is called to perform at the USA Music Awards, where she meets singer/songwriter Rafael. Later at the party, they meet again, and Rafael suggests they write a song. Dice orders Billie and her friends to leave, accusing Rafael of sexual advances towards Billie. Louise and Roxanne give Billie an ultimatum: them or Dice, but leave before she can choose. Billie cries, but is comforted by Dice as she laments "If you didn't believe in me, none of this would have ever happened."
The reconciliation is short-lived as Billie gets a threat from Timothy concerning the 100K debt that Dice failed to pay. Billie tells Dice that Timothy was at their apartment about his debt and her contract. She is confused because she thought he had handled her contract properly. She admits to Dice that Timothy threatened her and Dice, in a rage, puts Timothy in the hospital. In the middle of the beating, Dice is arrested, causing Billie to leave her appearance on Late Night Live to bail him out. Billie, upset about how Dice lied about her contract and his arrest, argues with and leaves him. With nowhere to go, she goes back to live with Roxanne and Louise.
Billie tries to deal with the pain by creating the single "Want You", with Rafael, which is a hit, but her emotional pain leads her to solo songwriting. Dice also misses Billie, and also begins writing a song. Billie goes to Dice's apartment in an attempt to reconcile. He's not home, but the music he has written is and Billie realizes they wrote the same song: "Never Too Far". She kisses the sheet music, leaving a lipstick imprint, which Dice later discovers. Dice plans a reconciliation, but is shot dead by Timothy. Billie's management and support crew see a report of the murder on television. They wonder if Billie was with him, they see that she is there and has seen the report. Billie onstage commands the band to stop playing "Loverboy," tells the crowd never to take someone for granted, and that if you love them, you should tell them, because you might never have the chance to tell them how you really feel. She then starts to sing "Never Too Far".
Afterwords, Billie reads a note Dice had left her, where he tells of his love for her, his plan to see her perform and that he has found Billie's mother. Billie's limo takes her to the secluded rural property where she is united with her mother once again.