Jane Kahn, a civil rights attorney who helped drive sweeping reforms in California’s prison system, died in her sleep last week of glioblastoma brain cancer. She was 64 years old.

Kahn worked at the San Francisco law firm Rosen Bien Galvan & Grunfeld LLP, where she focused on constitutional and civil rights law during a period of great turmoil in California’s prison system. She played a pivotal role in major court decisions that reshaped how inmates are treated.

“She saw the law and her work as something that had to move the ball of social justice forward, of remedying discrimination, remedying things she saw were failures in our society,” Kahn’s husband, Michael Bien, said. “She touched a lot of people.”

Kahn was involved in two lawsuits that began in the 1990s that found that California’s prisons provided inadequate mental health care to inmates and did not adhere to the Americans with Disabilities Act.

One of the lawsuits led to a landmark 2011 Supreme Court ruling that found that prison overcrowding had violated inmates’ constitutional protections against cruel and unusual punishment. The lawsuits prompted major reforms in California, including improvements in mental and medical health care and a reduction in the state’s prison population.

Kahn’s passion for helping the underserved and underrepresented carried over into all facets of her life, Bien said, whether it was caring for her children, volunteering in the community or working with nonprofits. When inmates wrote her letters asking for help, she often made it a point to respond — even if she could do little to help them.

“She walks into some prisons, and people start yelling, ‘Jane Kahn’s in the house, Jane Kahn’s in the house,’” Bien said. “And it’s not because she won these huge victories in court, it’s because she had an individual connection with these prisoners as people.”

Along with her work as an attorney, Kahn was also on the board of Camp Tawonga, lectured at conferences on mental health care in prison, and was a founding board member of the Prison University Project, a nonprofit that offers higher education classes to inmates at San Quentin.

The Prison University Project’s executive director, Jody Lewen, praised the tremendous impact Kahn had on the organization in a September speech.

“Through the sheer force of your personality, you have helped so many people inside and outside endure,” Lewen said. “And whatever their circumstances, and whatever the outcome, you’ve let thousands of people know that they were not alone.”

Throughout all her professional accomplishments, Kahn always prioritized caring for her family and friends, Bien said. Kahn is survived by her sisters, Debi and Julie, her brother, Michael, her sons, Ben, Max and Joey, and her daughters, Katy and Allison.

“She’s a woman who wrestled giants like the prison system and homelessness and so much more of what wasn’t fair in the world,” Kahn’s son, Joseph Bien-Kahn, wrote in a eulogy. “She would also fight any and every one who would say or do a thing to hurt us or hurt her friends.”

A memorial service was held Friday at the Sinai Memorial Chapel in San Francisco, which drew hundreds of friends and family from across the country. In lieu of flowers, the family requested a donation to Prison University Project, Hamilton Families or another charity.

Joaquin Palomino is a San Francisco Chronicle staff writer. Email: jpalomino@sfchronicle.com Twitter: @JoaquinPalomino