Ready starts with ready-witted Prem Kapoor (Salman Khan) helping his childhood friend Khushi (Zarine Khan) to elope with Raju (Ajay Devgn). Khushi’s intended bridegroom Gaurav (Arbaaz Khan) reveals that he also has a girlfriend, Kiran (Kangana 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 the wrong terminal to avoid meeting her. A young woman 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 pretends to be Prem’s intended fiancée. 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 to inherit 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.
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 marry. However, her uncle Suraj Chaudhary takes her away. Then the Kapoors come to know about her true identity; 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 CA Balidaan Bhardwaaj a.k.a. Balli (Paresh Rawal), a chartered accountant who serves 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. 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 gets the rest of his family to play 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 recovers from his coma, and reveals the truth about Prem. A physical fight follows, in which Prem gets the upper hand of Sanjana’s uncles and their men. He then explains to Amar and Suraj how Sanjana’s late mother wanted them to unite and get their niece married. The Chaudharies realise their mistake and are deeply apologetic for their 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’.