A transgender woman, she was born in Poston Relocation Camp, Arizona. As a young adult, Yamamoto struggled with her gender identity and decided to join the U.S. Army. She was awarded many medals, such as the National Defense Service Medal, Army Commendation Medal, and Vietnam Campaign Medal. After the army she attended UCLA'S School of Law, where she co-founded the Asian Pacific Islander Law Student Association. In 1984, she opened her own practice and has been working as a lawyer ever since. As a lawyer, her honors include an appointment by the Chief Justice of the California Supreme Court to serve on the Judicial Council Task Forces on Jury Improvement and Fairness and Access in the Courts. Yamamoto was a recipient of the 2013 Stonewall Award by ABA’s Commission on Sexual Orientation and Gender Identity.