In Joan Andersson's formative years she was heavily influenced by an exemplary set of parents whose progressive child rearing practices helped her mature without the strictures or role limitations that affected most young women of her generation. Her mother, a self taught Jewish intellectual, and her father, a leftist committed to civil rights struggles, raised her as a person with empathy for others and a internationalist world view.
A straight A student, Joan majored in psychology as an undergraduate at UCLA. One of her first acts of civil disobedience was to walk out of her graduation ceremony to protest the Shah of Iran, who was delivering the commencement address.
Joan went on study law at Yale University. There, for the first time, she was exposed to rampant sexism. Often fellow students and professors questioned the right of women to be at the prestigious university and to even practice law.
Back in Los Angeles, she and friend Dan Lund formed Lawyers for the People and became active in remaking and revitalizing the National Lawyers Guild, which had been foundering since McCarthy era witch hunts had decimated its ranks. Lawyers for the People was the precursor to the Bar Sinister, a law collective founded by Joan and Dan that defined itself as being in support of civil rights and peoples' struggles.
With the encouragement of mentor and radical lawyer Jean Kidwell, Joan represented the Black Panthers in a number of cases. When Joan was helping to plan an escape to Cuba for Black Panther leader Huey Newton, she met her future husband, Bill Zimmerman.
When the Bar Sinister broke up because of increasing sectarian politics, Joan left the collective to work on Tom Hayden's Senate race
After the Senate Race, Joan worked for two years as the supervising attorney for the Agricultural Labor Relations Board office in Oxnard. Joan and Bill then decided to have children. Joan made a controversial political decision for a feminist and radical lawyer. She decided to be the primary caregiver for her children while Bill worked to provide their livelihood.
While she gave up the practice of law to dedicate herself to her kid's upbringing, Joan remained politically active. She was a founder and member of the Board of Directors of Medical Aid to El Salvador. Once her children were older, she pursued a Masters degree in child development and served on the board of a charter school in South Central Los Angeles. She remained involved with the National Lawyers Guild, and for a time was the issue editor of the Guild Practitioner, the NLG law review.