Charlie Chaplin’s City Lights begins with the Tramp sleeping on a monument honoring "Peace and Prosperity," as it is unveiled to the public. He slides down the sculpture. He gets in a fight with two newsboys who taunt him for his clothes, then admires a nude statue in a shop window, getting into precarious slapstick scenarios along the way. On a street corner, he meets a beautiful blind flower girl, with whom he falls in love. As he walks away, a wealthy man slams the door of his limousine, which causes the flower girl to mistake the Tramp for a much wealthier man.
That evening, the Tramp goes to the river, where he finds a highly intoxicated Millionaire about to commit suicide. When he prevents the Millionaire from doing so, the Millionaire declares that he is forever indebted to him and they will be lifelong friends. He takes the Tramp back to his mansion, then out to a dance hall for dinner. The next morning they return home, and the Tramp sees the Flower Girl outside, gets some money from the Millionaire, and buys all her flowers. The Millionaire also gives the Tramp his car, and the Tramp drives the Flower Girl home in it.
When the Tramp goes back to the Millionaire's mansion, the Millionaire has sobered up and does not remember ever having met him. The butler, James, throws the Tramp out of the house. Later that night, however, when he is once again drunk, the Millionaire instantly recognizes the Tramp on the street and brings him home for a party. The next morning, the Millionaire, true to form, does not recognize the Tramp, and throws him out unceremoniously.
Meanwhile, the Flower Girl gets the flu and can no longer work to earn the rent for the apartment she shares with her grandma. In order to help them, the Tramp gets a job as a street cleaner, and promises to help her earn her rent. He also points out an article in the paper advertising a cure for blindness. When the Tramp goes back to work, he is late and gets fired.
Dejected, the Tramp wanders into an opportunity to make some easy money in a boxing match. While he first strikes a bargain with his opponent that they'll go easy on each other and split the winnings, his opponent soon has to make a run for it, and the Tramp is left to try his fate in the ring without an understanding. He is knocked out by his much more macho opponent and doesn't win the money.
Still determined to make the money for the Flower Girl's rent, the Tramp runs into the Millionaire on the street, who is drunk and so recognizes him. When they go back to the Millionaire's mansion, there are two robbers there. The Millionaire gives the Tramp $1000 to help the Flower Girl, and the Tramp is very grateful. Suddenly, however, the robbers attack the Millionaire and make a run for it before being apprehended by the authorities. When the police check the Tramp's person for stolen money, they find the $1000 and think he stole it. Luckily, the Tramp escapes and delivers the money to the Flower Girl, before telling her he has to go away for a while. The next day, he is arrested and locked up.
A few months later, the Tramp is released from jail, more disheveled than ever. With the money the Tramp gave her, the Flower Girl has opened her own flower shop and gotten her blindness cured. The Tramp wanders down the street and goes to pick up a crushed flower on the ground. When he turns around, the Flower Girl is there, affectionately laughing at his messy appearance, but she doesn't know who he is. He smiles at her as she gives him a fresh flower, and when she touches his hand, she instantly recognizes the touch, and realizes that he is the man who helped her and with whom she fell in love. He smiles at her, and the film ends.