In 1993, Erin Brockovich (Julia Roberts), a single mother grappling with the challenges of raising three children, faces a dire situation after a car accident involving a doctor who ran a red light. With her financial situation deteriorating, Erin finds herself in debt to the tune of $17,000 and without insurance, making her reliant on the outcome of her lawsuit. Unfortunately, her fiery demeanor during cross-examination backfires, resulting in a loss of the case. Her lawyer, Ed Masry (Albert Finney), initially optimistic about their chances, stops returning her calls, leaving Erin at a loss and struggling to make ends meet with only $74 left in her bank account.

Desperate for work, Erin confronts Ed at his firm, claiming he had assured her that things would improve. Moved by her plight, Ed offers her a position in his office. Despite her provocative style of dressing, which draws the ire of her co-workers, including secretary Brenda (Conchata Ferrell), Erin refuses to change her appearance. Life takes a turn when she meets George (Aaron Eckhart), a biker who becomes a source of support, especially when he helps care for her children.

As Erin digs into a seemingly routine real estate case involving the Pacific Gas and Electric Company (PG&E) and local resident Donna Jensen (Marg Helgenberger), she stumbles upon troubling medical records. Donna reveals that her family has been dealing with severe health issues, including Hodgkin’s lymphoma, and hints at a darker truth involving PG&E and their dealings related to Hexavalent Chromium. This prompts Erin to investigate further, uncovering evidence of toxic groundwater contamination that the company has attempted to downplay.

After a series of set-backs and moments of self-doubt—including a firing from Ed due to her absence and her deepening personal connection with George—Erin is reinstated, now with a raise. Her relentless pursuit of the truth leads her to win the trust of Hinkley residents, informing them of the dangers they face due to PG&E’s negligence. While Ed initially aims for a better sale price for the contaminated land rather than suing the corporation directly, Erin pushes for action as she uncovers more health cases linked to PG&E’s practices.

After months of hard work, Erin’s efforts culminate in a massive class-action lawsuit involving 634 plaintiffs, forcing PG&E to the negotiating table for a settlement. Amidst personal struggles, including George’s departure and the strain on her family life, Erin continues to rally the affected families. Her determination pays off when she receives crucial evidence from a former PG&E employee, further strengthening their case.

In a dramatic turn, a judge orders PG&E to pay a substantial settlement of $333 million to the plaintiffs. As Erin’s journey comes to an overarching conclusion, Ed presents her with a bonus she finds astonishing, finally recognizing her relentless commitment to seeking justice.