Robbie Hart is a wedding singer in Ridgefield, New Jersey in 1985, whose own wedding to his fiancée Linda is approaching. He meets and befriends Julia Sullivan, a new waitress at the reception hall where he works, and promises to sing at her wedding, though her fiancé, businessman and bond investor Glenn Gulia, has yet to set a date.

On Robbie's wedding day, his sister Kate informs him as he waits at the altar that Linda has changed her mind about the wedding, leaving him humiliated and emotionally devastated. Later that day, Linda visits Robbie and reveals that she fell in love with him for his ambitions of being a rock star, and hates the idea of being married to just a wedding singer. Robbie sinks into depression, causing his friends and family to be concerned. His best friend Sammy convinces him to return to work, but he gives a depressed performance that is panned, and decides to give up wedding gigs and reneges on his promise to sing for Julia when Glenn finally sets a date. However, Julia convinces him to help her with the planning and their friendship blossoms. During a double date with Julia, Glenn, and Julia's cousin Holly, Robbie learns from Glenn that he cheats on Julia frequently and plans to continue after they are married.

Julia and Robbie are increasingly confused by their deepening feelings for each other. When Holly tells Robbie that Julia is marrying Glenn for his money, he unsuccessfully pursues a job at a bank. Julia is dismayed at his materialism, and when he accuses her of the same, she becomes angry with him. Depressed, he decides to follow Sammy's example of only having shallow relationships with women, in response to which Sammy confides that he is unhappy, and encourages Robbie to tell Julia how he feels. Meanwhile, Julia confides in her mother that she has fallen out of love with Glenn and has developed feelings for Robbie, and bursts into tears thinking about becoming "Mrs. Julia Gulia". Robbie arrives to declare his feelings, and sees her through her bedroom window in her wedding dress, where she is happily looking in a mirror pretending she has just married Robbie, but Robbie assumes she is thinking of Glenn.

Heartbroken, Robbie leaves to get drunk and finds Glenn in the midst of his pre-wedding bachelor party, arm in arm with another woman. After a heated exchange, Glenn punches Robbie and mocks him. Robbie stumbles home to find Linda waiting for him wanting to reconcile, and passes out. The following morning, she answers the door and introduces herself as his fiancée to a crestfallen Julia. She runs to Glenn, who is sleeping off the events of the previous night, and tells him she wants to be married immediately. He half-heartedly offers to take her to Las Vegas.