JAI MUMMY DI is the story of two lovers whose mothers are sworn enemies of each other. Delhi-based engineering students, Puneet Khanna (Sunny Singh) and Saanjh Bhalla (Sonnalli Seygall), are in love with each other. Saanjh proposes to Puneet but the latter declines. He too wants to settle down with Saanjh but is afraid of his mother. That's because Puneet's mother Laali (Supriya Pathak) and Saanjh's mother Pinky (Poonam Dhillon) hate each other a lot.
Interestingly, they were the best of friends at one point and moreover, they reside next to each other. But they can't stand each other's sight. And Puneet is too scared to break the news that he's in love with the daughter of her 'enemy'. In anger, Saanjh breaks up with Puneet. She starts looking for suitable groom for marriage and even approves of Dev (Bhuvan Arora). Their marriage is fixed for October 16 at Diamond Hall in Noida.
When Puneet's mother Laali finds out that Pinky has managed to lock her daughter's wedding, she feels jealous. Not wanting to be left behind, she quickly selects a girl for Puneet, Sakshi. What's more, Puneet and Sakshi's marriage is also set on October 16 and that too in Diamond. Meanwhile, Puneet and Saanjh realize that they won't be able to stay happy with anyone else but each other.
Hence, they patch up and think of ways to bring their respective mothers together. When nothing works, they decide to elope and get married. What happens next forms the rest of the film.