With the encouragement of mentor and radical lawyer Jean Kidwell, Joan Andersson 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.