In 1989, Joy Mangano (Jennifer Lawrence), a divorced mother of two, struggles to make ends meet while working as a booking clerk at Eastern Airlines. She shares a cramped house in Quogue, New York, with her two young children, her mother Terri (Virginia Madsen), her grandmother Mimi (Diane Ladd), and her ex-husband Tony (Édgar Ramírez). The dynamic is tense, as Joy's father Rudy (Robert De Niro) and mother are divorced and can’t seem to be in the same room without erupting into conflict. Adding to her woes, Joy faces constant societal pressures from her overachieving half-sister Peggy (Elisabeth Rohm), who embarrasses Joy in front of her kids.
While Terri spends her days indulging in soap operas, leaving Joy to juggle household chores, only Mimi and Joy’s best friend Jackie (Dascha Polanco) truly encourage Joy's ambitions as an inventor. Despite having shown creative potential from a young age, Joy feels trapped in her chaotic family life and longs for independence. As a child, she had even designed a dog collar and a flea collar, but lacked the guidance to pursue patents.
The household is overly dependent on Joy’s meager contributions, with Rudy managing a garage that Joy assists with financially, while Peggy lends a hand in the business too. The situation grows more complicated as Tony, a former singer, shares the basement with Rudy. Initially drawn to Tony's dreamer persona, Joy soon finds herself overwhelmed as they welcome two children into a life where Tony proves to be often absent and intoxicated, leading to their eventual divorce.
As if the situation couldn’t worsen, after divorcing his third wife, Joy's father begins dating Trudy (Isabella Rossellini), a wealthy widow with business acumen. During a trip on Trudy's boat, a mishap with a glass of red wine results in Joy injuring her hands—a pivotal moment that sparks the inspiration for a self-wringing mop. With the help of staff at her father's garage, she advances her prototype and persuades Trudy to invest in this product, setting the stage for her entrepreneurial journey.
However, Peggy, ever the skeptical sister, questions Joy’s business acumen, arguing that her own decade of experience in the garage makes her more competent. Yet, Trudy connects Joy with a patent attorney who uncovers a potential legal quagmire involving a similar mop design owned by a company in Hong Kong. To thwart a possible lawsuit, Joy pays a hefty sum in royalties, but the ensuing chaos only intensifies when manufacturing flaws lead to increased bills.
Joy struggles to gain traction for her product as retailers resist carrying it, preferring to offer less reliable mops that necessitate repeat purchases. After a humiliating attempt to showcase her invention outside K-Mart, she is motivated to seek a new advertising avenue.
Through Tony's connections, she meets Neil Walker (Bradley Cooper), an executive at QVC. Impressed by her vision, Neil convinces her to manufacture 50,000 mops. To finance this production, Joy takes out a second mortgage on her home, despite the prior failures of infomercials. When the first TV spot flops, Joy pleads with Neil for another chance, emphasizing her precarious financial position. Fortunately, Joy’s television debut turns her product into a sensational success, aided by Jackie’s timely call during her broadcast that helps her regain her composure.
As Joy’s fortunes begin to shift, her grandmother’s sudden death and ensuing complications with family dynamics threaten to derail her progress. Peggy escalates the financial drama by paying unauthorized charges to the manufacturer, putting Joy's business at risk. Frustrated, Joy travels to California to confront the manufacturing contractor about the discrepancies and discovers fraudulent activities that have plagued her dealings from the start.
With tenacity, Joy navigates through the tangled web of contracts, ultimately reclaiming her molds and securing funds that validate her rights. The culmination of her struggles leads her to ample success as she becomes a prolific inventor with a portfolio of over 100 patents. In the end, even if family tensions remain—particularly as Rudy and Peggy contest her ownership of the company—Joy rises to champion her own narrative, helping to inspire future generations of inventors, including a young mother she mentors.
