In the year 1956, Ruth Bader Ginsburg (Felicity Jones) is one of six women in her class at Harvard Law School. Her husband Martin (Armie Hammer) helps her get ready for a dinner at the Dean’s house welcoming the women to the class. When she arrives, Dean Griswold (Sam Waterston) callously makes each of the women stand up and explain why they’re in law school. Ruth remains unfazed – she continues excelling in classes, and when men like Professor Brown (Stephen Root) won’t call on her, she still manages to make her points.
While playing charades at a social gathering with friends, Martin doubles over in pain. At the hospital, the doctor explains that he has testicular cancer and that the chances of survival are at six percent. Ruth assures Martin that he’s going to live. She begins attending Martin’s law school classes in addition to her own, typing both of their essays, and taking care of sick Martin and their young daughter Jane.
Martin recovers fully from the cancer. He gets a job in New York, and Ruth meets with Dean Griswold to see if she can continue to earn her Harvard degree long-distance. Though he has made exceptions for men in the past, he coolly refuses, saying she has no special circumstance, and Ruth transfers to Columbia. Despite having graduated at the top of her class and being editor of the law review, no New York firms will hire her because she’s a woman. She is frustrated and unable to use her law degree she worked so hard for. She is offered a Professorship, to teach law. Martin insists she decline, saying she will get a job and she shouldn’t settle – she wanted to practice law. But Ruth decides for her family she will take the job.
In 1970, Ruth is now a respected and successful professor. A lot of her students are young women who are involved in women’s lib movement. She teaches her students about a case Dorothy Kenyon argued, where a jury of all men convicted a woman. Kenyon argued it was unconstitutional, that the woman should have a jury of peers – meaning women as well – and that it was gender discrimination. The court didn’t believe gender discrimination was a real thing, and she lost. When she gets home, her now teenage daughter Jane (Cailee Spaeny) tells her mom she got an A on her ‘To Kill a Mockingbird’ essay, but Ruth admonishes her that Atticus Finch is not a good lawyer, since he helped cover up a murder at the end of the story. Frustrated at her mother being a stickler, Jane lashes out and runs to her room. Martin comforts Jane, explaining that Ruth is the way she is because her mother died when she was young and pushed Ruth to always be her best.
Martin, a tax attorney, finds a tax case and brings it to Ruth. She says she’s not interested, but he urges her to take a closer look: Charles Moritz filed for a caregiver tax deduction because he was caring for his ailing mother, but he was denied and prosecuted over it because that deduction is only available to women. Ruth realizes this is a case of gender discrimination where the victim is a man. She knows it could be massively important to helping repeal gender discrimination everywhere. She goes to meet old friend Mel Wulf (Justin Theroux), now the legal director of the ACLU (American Civil Liberties Union) and urges him to help her take on the Moritz case. He sympathizes but thinks it’s unwinnable and is busy with many racial discrimination cases. Ruth is resolved to take it, however, and despite the fact that she’s never practiced law, as a law professor she can legally take the case. Martin gets permission from his job to take a side project, and Ruth flies to Denver to meet with Moritz (Chris Mulkey). He is just trying to take care of his mother and doesn’t think it’s fair that the government is calling him a crook. Ruth agrees and promises to do everything she can.
After another fight with Jane, who is into the women’s lib movement and doesn’t think her mother is doing enough, Ruth takes Jane to meet the famous Dorothy Kenyon (Kathy Bates). Ruth tells Dorothy about the case, and while Dorothy is interested and wishes Ruth well, she doesn’t think the law will change until the culture changes. Despite that, Dorothy goes to Mel and argues him to take on Ruth’s case.
Mel tells Ruth the ACLU is going to back her case. He arranges a mock trial run in Ruth’s apartment. During the questioning from the mock judges, Ruth, who has never been a practicing lawyer, struggles with the aggressive questioning – she’s not a flashy speaker, she’s quiet and measured. Mel tells Ruth that Martin is going to argue the case with her – he’ll argue the tax law, and she’ll argue the gender discrimination. Martin is reticent to take any of the cases from Ruth, but Mel says it is not a choice, the decision has been made.
Meanwhile, Griswold has moved up at is now working at the state along with Brown. They will be opposing Ruth in the Moritz case. Griswold urges them that this case has the fate of the American nuclear family in its hands, and losing it would be a slippery slope to letting the traditional family fall apart.
Before the Moritz case goes to trial, Wulf tells Ruth that the ACLU has taken another gender discrimination – Sally Reed, a woman who attempted to be the administrator of her dead son’s estate but wasn’t allowed because the law stated: “males were preferred.” Wulf thinks they have a good shot at winning and wants Ruth to settle the Moritz case because if they lose it, it will set a precedent that will stop them from winning any cases. Ruth is angry, wanting to fight for what’s right, but Wulf tells her the settlement arranges haven’t been made. She tells Moritz, but he is disheartened when it’s clear the state isn’t going to clear his name and say he didn’t do anything wrong. Ruth meets with Griswold and Brown, and turns down their one dollar settlement offer. She insists on a larger sum and that the state admit it was gender discrimination. They balk completely, and so the case heads to trial.
At court, Ruth and Martin make their arguments, and the judges are pretty tough on them, barely believing that gender discrimination even exists. When opposing counsel gets up for their arguments, they go after Ruth and Martin personally, accusing them of trying to incite “radical social change.” Ruth decides to handle the rebuttal – she tells the court that radical social change is already happening. She’s seen how her daughter is living a different life than she could, and that the world is continually changing, and the law should allow for that. She asks them to right the wrong that is in the law.
The Ginsbergs leave the trial, happy but awaiting the results. The final on-screen text tells us that Ruth won the Moritz and Reed cases, and started the women’s branch of the ACLU. Martin continued to be a renowned tax attorney, and Ruth was eventually appointed to the supreme court by a vote of 97-3. In the movie’s final shot, Felicity Jones as Ruth walks up the steps up the supreme court building, and it cuts to newsreel footage of the real-life Ruth Bader Ginsberg walking up the very same steps.