Plot:
The film starts with a Muslim family watching TV in Sultanpur village, Azad Kashmir, Pakistan and an expectant mother's (Meher Vij) baby kicks when Shahid Afridi leads Pakistan to victory in an India–Pakistan cricket match. A few years later, the baby grows up to be a young speech-impaired girl, Shahida (Harshaali Malhotra). Her mother takes her to Hazrat Nizamuddin Auliya's Dargah inDelhi, India, to pray for her speech to return.
On their way back, in the middle of the night, right next to the Pakistan border, the train in which Shahida and her mother were traveling suddenly stops. While everyone is asleep she leaves the train to play with a lamb she saw stuck in a small ditch. The train starts as Shahida is playing with the lamb. She runs to catch it, but, realizing that she cannot, she tearfully watches the train cross through the border into Pakistan. Lost in India, she boards a freight train, reaching Kurukshetra.
In Kurukshetra, a Brahmin devout Shri Hanuman named Pawan Kumar Chaturvedi, also known as Bajrangi (Salman Khan), is dancing merrily with other worshipers. He feeds Shahida and she starts following him. Since she is fair-skinned, he assumes that she is a Brahmin. He buys her a Bajrang Bali pendant to protect her from harm. On the bus ride to Delhi, Bajrangi quizzes the little girl, and calls her Munni (Little Girl) to find out which city she's from, but she doesn't respond to any Indian town names. He asks her to call him "Maama" (maternal uncle) when she starts speaking. When he is asked by a fellow passenger about how he moved from his hometown of Pratapgarh to Delhi, Bajrangi told the passengers his life story.
Bajrangi narrates how he was a failure during childhood, and that it took him 20 years to earn his high school diploma. His father died of shock when he told him that he had finally passed. He moved to Delhi because it was his father's last wish that he leave him and stay there with a man named Dayanand, (Sharat Saxena) in order to find his own job. He tells the story of how he met a woman named Rasika (Kareena Kapoor) in Delhi; they met when a ticket collector on a bus asked Bajrangi to equally split a note of 10 rupees between Rasika and himself. When they got off the bus he persistently followed her. Exasperated, Rasika asked him to get change from a stall selling water bottles. While he is getting the change, she leaves.
Bajrangi eventually locates the place where Dayanand lives and finds him holding a wrestling competition there. Rasika — who also lives in the same building because she is Dayanand's daughter — sees Bajrangi with Dayanand. She claims that he had stalked her there and was harassing her. The other wrestlers grabbed Bajrangi, who managed to introduce himself as Pawan. Dayanand has him released and brought to stay in his house. Najrangi and Rasika gradually fell in love. When Rasika refused a marriage proposal in favor of Bajrangi, Dayanand said that he would have to prove himself worthy of Rasika. In order to gain Rasika's hand in marriage, he would have to find a decent job and buy a decent house in six months' time.
In present time, Bajrangi and Munni finally arrive in Delhi, and she is welcome in Dayanand's house. Munni quickly befriends everyone there and is accustomed to being part of the household. One day, at lunchtime, Munni manages to slip away unnoticed. They track her to their next door neighbors' house, where she is eating meat. Bajrangi is then convinced that she is not a Brahmin, but in fact a Kshatriya. One day, while Bajrangi, Rasika, and Munni are outside shopping, Munni steals bangles from a stall. Bajrangi then makes her return them and makes her pray to Bajrang Bali for forgiveness. While he is lost in prayer, Munni once again manages to slip away. Bajrangi sees Munni enter a mosque and tries to stop her. Once he finds Munni wrapping a hijab around her head and praying in the mosque, he realizes that she is a Muslim. This makes him nervous as he knows that Dayanand is hateful of non-Hindus. Rasika says that they should keep it all a secret. However, her plans are foiled when Munni cheers at Pakistan's victory during an India-Pakistan cricket match and kisses the Pakistani flag on the TV. Everyone is shocked to learn that she is a Pakistani. Dayanand then says that she is not welcome in his house and that Bajrangi will have to send her home immediately. They visit the Pakistani embassy, but a violent protest forces the authorities to shut it down for a month.
He strikes a deal with a travel agent and uses the money he has been saving for the house to pay the agent, who promises to find a route to her home that will not require a visa. However, Bajrangi is devastated to learn that the agent had in fact taken her to a brothel. He beats everyone involved and than takes Munni back with him, vowing to bring her home on his own. With great difficulty, they manage to get the Pakistani army's permission to cross the border. Shortly after arriving in Pakistan, Bajrangi is arrested on the grounds that he is an Indian spy. At the police station, Munni sees a scenic photograph on a calendar, indicating that she comes from that area. Bajrangi beats several policemen and escapes from their custody because one of them had mistreated the girl. He meets Chand Nawab (Nawazuddin Siddiqui), a journalist working for a Pakistani TV channel, who initially thinks that Bajrangi is an Indian spy. He soon realizes his mistake and joins Bajrangi in the noble task of finding Munni's parents. The police are after them, but they manage to hide themselves in a madrassa. The head of the madrassa turns out to be a nice person and helps them in their quest. Bajrangi shows him the photograph to know where the girl was from. He tells them that it could be in Pakistan-administered Kashmir. He even helps them avoid capture by the police.
Upon reaching Kashmir, they visit a shrine. Munni's mother is also praying there, but they do not meet. Chand leaves the shrine to make a few calls. He contacts a number of TV channels to tell them the story of Bajrangi, but they refuse to air it. He decides to film a video of himself telling the story, and uploads the video on YouTube. While watching this video on Chand's camera, Munni recognizes her mother walking by. The footage showed her get off the bus. With the help of a driver, who calls out the name of previous bus stops, they find out Munni's mother had boarded the bus from Sultanpur, to which Munni raises her hand, finally identifying her home.
They leave for Sultanpur by bus. On their way, they spot a group of policemen, that are about to check their bus for Bajrangi. Bajrangi devises a plan to get the polices' attention. He gets off the bus and creates a scene. Once the police visually identify him as "the Indian spy", he flees. When the officers catch him, they beat him. He runs away again, and just as he is about to escape, he is shot and falls into a river. Meanwhile, Chand and Munni find Sultanpur, where Munni is finally reunited with her mother. Bajrangi is revealed to be alive, and held hostage in a police station, where the Pakistani officers are brutally torturing him.
The video uploaded by Chand goes viral throughout India and Pakistan. A compassionate senior officer realizes that Bajrangi is innocent, and has him released, defying the orders of an even higher ranked officer who is bent on getting him jailed. Thousands of Pakistanis come to see Bajrangi off. They cheer him on by shouting "Bajrangi Bhaijaan". Shahida is also in the crowd. As Bajrangi is about to enter India, she comes forward, and calls out, "Jai Shree Ram, Maama!" Bajrangi, managing to hear her voice over the thousands of cheering Indians and Pakistanis, looks back. They run towards each other and embrace.