The film starts with ready-witted Prem (Salman Khan) helping his sister-in-law Khushi (Zarine Khan) to elope with Raju (Ajay Devgn). Khushi's intended bridegroom Gaurav (Arbaaz Khan) reveals that he also has a girlfriend, Kiran (Kangna Ranaut), whom he wants to marry. The elopement angers Khushi's father, Mr. Pathak (Mithilesh Chaturvedi) and Prem's family, the Kapoors. Prem manages to pacify his family members.
The Kapoors decide to get Prem engaged to Pooja. Prem is sent to receive Pooja at the airport; however, he deliberately goes to he wrong terminal to avoid meeting her. A girl named Sanjana (Asin), who has just run away from her own wedding, overhears Prem telling his uncle about ditching Pooja. Since nobody from Prem's family has ever seen Pooja, Sanjana herself pretends to be Prem's intended fiancee. Sanjana, posing as Pooja, goes to stay with the Kapoors and wins the hearts of the entire family, except Prem, who gets irritated with her.
Meanwhile, Sanjana's maternal uncles, Amar Choudhary (Akhilendra Mishra), and Suraj Choudhary (Sharat Saxena), who are rivals, try to search for her. Each uncle wants Sanjana to marry his respective brother-in-law in order to grab her wealth. Sanjana and Prem escape from Suraj Chaudhary's goons by taking a lift in the car of Mr. Lehri (Sudesh Lehri). Prem outwits the goons and sends Suraj's son Aryan into a coma while escaping. Suraj Choudhary takes the help of Mr. Lehri to get to know who ran away with Sanjana.
But by then, Prem finds out Sanjana's true identity, and she tells him about her uncles trying to get her married. Prem and Sanjana fall in love and decide to get married. However, her uncle Suraj Chaudhary takes her away. Then the Kapoors come to know about her true identity; however, they still want her as Prem's wife. Prem assures Sanjana that she should stay with her uncle, and he will find a way to marry her as well as reunite her whole family.
Prem pretends to be the nephew of Balidaan Bhardwaaj a.k.a Bali (Paresh Rawal), a Chartered Accountant who serves both of Sanjana's uncles. Prem convinces Suraj and Amar Chaudhary not to get either of their brothers-in-law married to Sanjana. Instead, he suggests the daughters of America's billionaires K.K Modi and B.K Modi as suitable brides for the two brothers-in-law. What the Choudharies do not know is that K.K and B.K Modi are actually Prem's dad and uncle in disguise. Prem also gets the rest of his family to play various characters, to trick Sanjana's family into letting her marry him. He also manages to change the Chaudhary family's negative attitudes.
But on the wedding day, Aryan comes out of coma, and reveals the truth about Prem. There is some fighting, in which Prem gets the best of Sanjana's uncles and their men. Then he tells Amar and Suraj Chaudhary how Sanjana's late mother wanted them to unite and get their niece married. The Chaudharies are deeply apologetic for their bad behaviour. In the end, Prem and Sanjana get married and their wedding picture is taken with the Kapoors and Chaudharies, a.k.a. the 'Chapoors'.