In 1987, 16-year-old Precious (Gabourey Sidibe) lives in the Harlem neighborhood of New York City with her unemployed mother Mary (Mo’Nique), who has long subjected her to physical, verbal, and sexual abuse. Precious has also been raped by her now-absent father, Carl (Rodney “Bear” Jackson), resulting in two pregnancies. The family resides in a Section 8 tenement and survives on welfare. Her first child, daughter Mongo (short for Mongoloid), has Down syndrome and is being cared for by Precious’ grandmother, though Mary forces the family to pretend that Mongo lives with her and Precious so she can receive extra money from the government. When Precious’ second pregnancy is discovered, her high-school principal arranges for her to attend an alternative school, where she hopes Precious can change her life’s direction. Precious finds a way out of her traumatic daily life by escaping into daydreams in which she is loved and appreciated.

Inspired by her new teacher, Blu Rain (Paula Patton), Precious finally learns to read and write. She meets sporadically with a new social worker Ms. Weiss (Mariah Carey), who learns about the sexual assault in the household when Precious reveals who fathered her children. While Precious is in the hospital giving birth to her second child Abdul, she meets John McFadden (Lenny Kravitz), a nursing assistant who shows her kindness and develops a crush on him. Upon returning home, Mary asks to hold Abdul. When Precious’s back is turned, her mother tosses the baby aside and attacks her, angrily declaring that Precious’ revelation about the abuse has resulted in them being cut off from welfare. Precious fights back and runs away with Abdul, while Mary tries to drop the television set on them; she eventually breaks into her school classroom for shelter. When Ms. Rain discovers them the next morning, she frantically calls local shelters looking for a safe place for Precious and Abdul to stay, but they end up staying with Ms. Rain and her live-in girlfriend. The next morning, Ms. Rain takes her and Abdul to find assistance for them; Precious will be able to continue her schooling while she raises Abdul in a halfway house.

Mary soon returns to inform Precious of her father’s death from AIDS. Precious later learns that she is HIV-positive, though Abdul is not. Feeling dejected, she steals her case file from Ms. Weiss’s office. As she shares the details of her file with her fellow students, she begins to hope for the future. Later, Precious meets with her mother, who brings Mongo, at Ms. Weiss’s office. Ms. Weiss confronts Mary about her and Carl’s abuse of Precious, going back to when Precious was 3 years old. Mary tearfully confesses that she’s always hated Precious for “stealing her man” by “letting him” abuse her, and for eventually “making him leave.” Precious tells Mary that she finally sees her for what she is, and tells her mother that she will never see her or the children again, leaving with Mongo and Abdul. Mary begs Ms. Weiss to retrieve her daughter, but Ms. Weiss silently rejects her and walks away.

Precious plans to complete a GED test to receive a high-school diploma equivalency. She walks out into the city with both children in tow, ready to start a new life and have a brighter future.