Bundle of Joy is a Technicolor musical remake of the comedy film Bachelor Mother (1939), which starred Ginger Rogers. It stars Eddie Fisher and Debbie Reynolds (who were married in real-life at the time), and Adolphe Menjou. An unmarried salesgirl at a department store finds and takes care of an abandoned baby. Much confusion results when her coworkers assume the child is hers and that the father is the son of the store owner.
Polly Parish (Reynolds) works in the Millinery Department at J.B. Merlin & Son's department store on the Upper East Side of Manhattan. She is summoned to the office of the store manager, who informs her that she is fired because she is overselling hats, which creates too many returns and too much work for the accounting department. After work, Polly walks home and wonders what she will do to make ends meet.
On a step, she finds an abandoned baby in a blanket and instinctively picks it up to comfort it. As she bends over, the door behind the step opens and a woman ushers Polly and the baby inside. Polly has not noticed the sign that indicates the door belongs to an orphanage. When she denies the baby is hers inside, the staff disbelieve her, having experienced countless women ashamed to admit that they bore a child out of wedlock. Polly explains that she has just lost her job at J.B Merlin & Son's and insists there is no way that she will care for a baby that is not hers.
After she leaves, the head of the orphanage decides to intervene on her behalf, knowing the Merlins to be charitable. He convinces the firm to hire Polly back, and she is summoned to a meeting with Dan Merlin (Fisher) the son of the titular owner. Dan informs her that she will be hired back at $10 more per week and that a gift will be delivered to her apartment later that night. When the baby arrives, Polly is flabbergasted. She convinces a friend to help her deliver the baby back to Dan at his home on East 63rd Street.
They leave the baby in the care of Dan's butler, whom Dan enlists to help him return the baby to Polly. They track her down to a dance hall where she is hoping to win a prize. Dan gets into a scuffle and gets thrown out. So he goes to Polly's apartment and waits for her there with the baby. Forced to care for the baby, Polly makes do and grows fond of him. She names the child John, and Dan checks in on her from time to time.
On New Year's Eve, Dan is stood up by his date, because he had forgotten to call her earlier. He arranges for Polly's landlady to watch John while they go out together. He takes her to the department store to get an outfit for a night out on the town. When he drops her off back at home, he jokes that she is fired so that he can kiss her.
Meanwhile, J.B. Merlin has been misinformed that he is a grandfather, mistaking John to be Dan's son. He begins to make arrangements for Dan to have full custody of the child. Polly panics at the thought of losing John. So she pretends that her landlady's nephew, who is visiting from Harvard, is John's real father. Dan produces a store employee to pretend he is the father. The ensuing confusion leads to a full confession of love from Dan and a happy union for the new family, and J.B. is convinced the boy is his grandson.
- Eddie Fisher as Dan Merlin
- Debbie Reynolds as Polly Parish
- Adolphe Menjou as J. B. Merlin, Dan's father and Polly's ultimate boss
- Tommy Noonan as Freddie Miller
- Nita Talbot as Mary
- Una Merkel as Mrs. Dugan
- Melville Cooper as Adams
- Gil Stratton as Mike Clancy
- Bill Goodwin as Mr. Creely
- Howard McNear as Mr. Appleby
- Robert H. Harris as Mr. Hargraves
- Mary Treen as Matron
- Edward Brophy as Dance Contest Judge (as Edward S. Brophy)
- Scott Douglas as Bill Rand