D. N. Tripathi (Piyush Mishra), a lyricist, attempts to write a biography on Sanjay "Sanju" Dutt (Ranbir Kapoor), comparing him with Mahatma Gandhi. A flabbergasted Sanjay has him thrown out. The Bombay High Court delivers its verdict regarding the 1993 Bombay bombings and sentences Dutt to five years jail term for violating the Arms Act. Manyata Dutt (Dia Mirza) approaches Winnie Diaz (Anushka Sharma), a London-based writer, to write Sanjay's biography and present his version of his life to the public. Although unwilling at first, Winnie is asked by Zubin Mistry (Jim Sarbh), a real estate builder to not write the biography, which intrigues her. Winnie first interviews Sanjay, and his life is revealed in a flashback.Sanjay's father Sunil Dutt (Paresh Rawal) plans to launch his acting career in Bollywood with the film Rocky (1981) (Sunil Dutt is the director). Upset over his father's controlling behavior on set (Doesnt allow him to smoke cigarettes), Sanjay is encouraged by his friend Zubin "God" Mistry to try drugs for the first time. Sanjay soon discovers that his mother Nargis (Manisha Koirala) is suffering from cancer and is taken to New York for treatment. This incident furthers his descent into alcoholism and drug addiction.He meets Kamlesh (Vicky Kaushal), a fan of Nargis, in New York, and they become quick friends. Kamlesh prays for Nargis's quick recovery & wins over Sanju. Kamlesh manages to make Sanjay stay his addiction. Nargis recovers and the family returns to Mumbai. After learning of his girlfriend Ruby's (Sonam Kapoor) fixed marriage due to his ongoing drug addiction, Sanjay relapses. Kamlesh convinces Ruby to register marry Sanjay; Moved by his devotion Ruby shows up at the registrar office at 4 pm the next day, but upset with his intoxicated behavior, she leaves him. Nargis passes away three days before the release of Rocky, which takes an emotional toll on Sanjay. Sanjay agrees to attend a rehabilitation center in the United States, and eventually recovers with the help of his father and Kamlesh. On returning to India, he meets with Zubin and beats him for selling him drugs. Zubin was taking glucose powder while selling expensive drugs to Sanjay.The later part of Dutt's life is narrated by his now-estranged friend Kamlesh, who Winnie tracks down. In the 1990s, Sanjay turns to bodybuilding and his career in Bollywood has greatly improved. After the 1992 Babri Masjid demolition, Sanjay acquires three AK-56 rifles to ensure the protection of his father, who had by then ventured into politics, and sister, Priya Dutt (Aditi Gautam). He and his family had been receiving death threats for Sunil's work on helping Muslims during the riots, right after the Babri Masjid demolition. A series of bombings occur in Bombay shortly thereafter. Sanjay is arrested in 1993 for possession of illegal arms supposedly supplied by the D-Company to be trafficked for protection during potential communal rioting after the bombings.Sunil Dutt fights the case in SC and gets bail for Sanju after 452 days. He approaches a lot of politicians, but no one wants to get involved with TADA. Then news emerges of Sanju's involvement with supplying RDX for the blasts. Sanjay is convicted and sentenced to imprisonment for five years under Terrorist and Disruptive Activities (Prevention) Act (TADA), threatening his career. Indian media labels him as a terrorist, further tarnishing his public image. Believing Sanjay to be guilty, Kamlesh severs ties with him.After his release in 1997, Sanjay appears in a string of flops. When his popularity had begun to wane, he is signed for the title role in Munna Bhai M.B.B.S. (2003), co-starring his father (Sunil recommends the script to Sanju and thinks working together will help discipline him). Sanjay's performance garners him the Filmfare Award for Best Performance in a Comic Role and his public image improves, making his father proud. Shortly afterwards, his father passes away. In 2006, the Bombay High Court finds Dutt guilty under the Possession of Arms Act, while not finding him to be a terrorist.In 2013, he is arrested again by the same verdict upheld by the Supreme Court of India. Sanjay convinces Winnie and Kamlesh of his innocence by blaming the media for falsely accusing him of terrorism (he argues that the RDX truck that media accuses him of, was never ever parked at his house. Even his charge-sheet and conviction did not mention anything about RdX), and is subsequently released from prison in 2016. Sanjay finds out that Winnie has completed writing his biography, titled Kuch Toh Log Kahenge (translation: People will keep saying something), named after one of his father's favorite songs. He and his family reconciles with Kamlesh.