The movie start by introducing a twice-divorced, unemployed mother of two young children and an infant, consults lawyer Ed Masry (Albert Finney) of the Van Nuys, a California firm Masry and Vititoe, as her effort to claims for injuries she suffered in a car accident that was not her fault, her name is Erin Brockovich (Julia Roberts). Ed assures her that he can get her a large settlement, unfortunately he loses the case. Erin's bank balance stands at $74 after the incident; she struggled to get herself a job with limited budget to rise up her 2 children and a baby.
She eventually force her way into a job at Ed’s firm as a file clerk, Erin also meets a new neighbor, George, who has a passion for motorcycles and whom her children adore. One day, while filing, Erin comes across a pro-bono case against the San Francisco-based Pacific Gas & Electric Co. (PG&E) that Ed is handling on behalf of residents of Hinkley, California. Erin ask Ed if she can assist with the case, in which Ed agrees and Erin rightaway drives to Hinkley.
The Jensens family who live at Hinkley suspect that hexavalent chromium, known as Chromium 6 that being use by the PG&E plant may be the cause of their illness. When Erin returns to Ed's office, she is being surprised by the condition that she has been fired, as Ed had misunderstood what Erin was doing. Ed visits Erin who is still unemployed, to inform her that the UCLA professor has examined the papers she found in Hinkley and concluded that the levels of chromium there could be responsible for the cancer in the Jensen family.
Ed apologizes to Erin and, after she inform him with her other discoveries, Ed is being persuaded to rehire her, with a raise and benefits. Ed and Erin then go to Hinkley, meet with other residents and inform them that his firm will represent them against PG&E. If they win the case, his fee will be forty percent of whatever is awarded, but if they lose, his fee will be zero....