In 1927 Kansas City Pete Kelly and his jazz band play nightly at a speakeasy. A local gangster starts to move in on them and when their drummer is killed Kelly gives in, even though this also means taking the thug's alcoholic girl as a singer. Kelly soon realises he has made a big mistake selling out in this way and that rich girl Ivy is now the only decent thing in his life.
In Hollywood of the 50's, the obscure screenplay writer Joe Gillis is not able to sell his work to the studios, is full of debts and is thinking in returning to his hometown to work in an office. While trying to escape from his creditors, he has a flat tire and parks his car in a decadent mansion in Sunset Boulevard. He meets the owner and former silent-movie star Norma Desmond, who lives alone with her butler and driver Max Von Mayerling. Norma is demented and believes she will return to the cinema industry, and is protected and isolated from the world by Max, who was her director and husband in the past and still loves her. Norma proposes Joe to move to the mansion and help her in writing a screenplay for her comeback to the cinema, and the small-time writer becomes her lover and gigolo. When Joe falls in love for the young aspirant writer Betty Schaefer, Norma becomes jealous and completely insane and her madness leads to a tragic end.