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In 1986, Rayappan, a Tamil Nadu MLA of the ruling party, is delivering a speech at J.K. Nagar, an impoverished suburb in Chennai, where one of the attendants, a pregnant woman, goes into labour. As a publicity stunt for creating sympathy, Rayappan orders his men to help the woman by lending their dhotis. The woman gives birth to a boy, whom Rayappan christens as Singaravelan, or "Singam" on the stage. Singam grows up as an orphan as his mother had died shortly after the birth of his younger sister, Manimegalai, followed by the death of his father due to overdrinking. Singam’s relationship with Manimegalai is quite fraught and strained as the former blames her for their parents death and the latter disapproves of the former's obsession towards Rayappan, for whom he even sold her mother’s only nosepiece for party promotions. This led them to not be on talking terms for 20 years.

In 2021, Rayappan, now a powerful and influential politician, begins scouting for a suitable candidate to work as a councillor for J.K. Nagar. Vying for attention, Singam strives to seek Rayappan's consideration by performing a media stunt by drinking poison in front of press during Rayappan’s arrest and gains his trust, much to the irritation and dismay of Mangalam, Rayappan's right-hand man, who is also vying for the position. Singam manages to emerge as Rayappan’s favourite within a short span of time by employing hilarious techniques and his friend Vasu’s ideas. Frustrated at being sidelined, an infuriated Mangalam brandishes a bottle at Singam's head; he is subsequently expelled from the ruling party for his ruthless behaviour.

Shortly after the incident, Singam develops an alter ego, presumably from his injuries who does quite the opposite of Singam’s doings. Next day he gets nominated for the counsellor chair, but beforehand Rayappan asks for 50 Lakhs as a deposit for his post, which he got from duping Kamatchi (Raashi Khanna), a wealthy daughter of a moneylending businessman who Singam initially kidnapped with Vasu as pawn for extorting money from her father with the help of Vasu’s hired goons, only to be saved by his alter ego who first resurfaces by thrashing the goons and saving her. During elections, both Singam and Mangalam try various corrupt tricks to lure the voters and increase their vote bank. Initially, Singam is lagging behind in public opinion and votes due to the lack of money power but manages to gamble on the sympathy by intentionally carrying a pregnant woman Lakshmi in front of the people to gain voters recognition and trust of the people very much to horror and dismay of Vasu but ultimately beats Mangalam to become the new counsellor of J.K Nagar.