In 1958, Margaret, portrayed by Amy Adams, makes the bold decision to leave her husband, taking her young daughter, Jane (played by Delaney Raye), to the vibrant North Beach area of San Francisco. As a single mother, Margaret supports her family by working to create illustrations at a furniture factory. There, she finds camaraderie with her friend, Dee-Ann (Krysten Ritter), who assists her in settling into their new life.
While showcasing her talent at an outdoor art show, Margaret crosses paths with Walter Keane (played by Christoph Waltz), a man selling his charming Parisian street scene paintings. While Margaret offers her live portrait sketches at just one dollar, Walter advises her against underpricing her art. His charismatic personality wins over both Margaret and Jane, leading to idyllic dinners and dreams of a future trip to France, all the while boasting of his artistic education in Paris.
Margaret’s unique style, characterized by girls with oversized eyes, results in artworks signed simply with the name KEANE. However, complications arise when her ex-husband serves her with court papers seeking custody of Jane. Walter, smitten, soon proposes, and they marry amidst turmoil.
Walter pursues the art scene vigorously, showing their work to Reuben (Jason Schwartzman), an unimpressed gallery owner who refuses to display their pieces. Undeterred, Walter tries to make a name for himself at a local jazz club but ends up in a violent clash over inadequate wall space—an event that captures headlines and entices crowds to witness the art that sparked a brawl.
The story gains momentum as celebrity gossip columnist Dick Nolan (Danny Huston), who provides narration, becomes intrigued, but he primarily seeks out Margaret’s distinct paintings rather than Walter's claims. Walter, eager for fame, begins to market their works as his own, leading to an explosion of sales and the opening of his own Keane gallery, where he produces inexpensive reproductions of Margaret’s art.
While their lifestyle flourishes, with a move to an opulent mansion, Margaret feels increasingly isolated, locked away while Walter mingles with A-listers. The facade of their relationship begins to fray, as Walter insists on misleading their daughter Jane (Madeleine Arthur) about the true authorship of the paintings. Enraged by Walter’s appropriation of her work, Margaret attempts to change her artistic style to regain her identity as a painter.
A troubling discovery leads Margaret to find paintings of Parisian scenes signed by another artist, revealing Walter’s deceptive talents. When confronted, Walter admits his inability to paint but warns Margaret to remain silent about the truth. As tension escalates between them, Walter's threats of violence compel Margaret and Jane to flee, culminating in a dramatic escape during a fiery incident instigated by Walter.
Their new life begins in Honolulu, Hawaii, where Walter makes demands in exchange for a divorce, leaving Margaret feeling trapped. With newfound clarity inspired by two Jehovah's Witnesses, she decides to reclaim her identity by signing her paintings with "MDH Keane." A surprise radio interview shocked the world, as Margaret publicly declares herself the real artist, which swiftly captures national attention.
As Walter’s fevered denials continue, Margaret counters with a lawsuit for defamation against him and the press, resulting in a courtroom spectacle. The judge challenges both to create a piece of art under time constraints, where Margaret showcases her undeniable talent while Walter falters under pressure, leading to her triumphant victory in court.
Outside the courthouse, Margaret expresses that her true desire is for recognition, not riches. Amidst the media frenzy, she signs a publication, finally taking ownership of her work. Walter, holding onto his delusions until his death in poverty, never paints again, while Margaret rejuvenates her passion by returning to San Francisco to open a new gallery, continuing to create art every day.
