Opponents to the bill say it legalises premature suicide, with religious organisations claiming it allows doctors to prescribe life-ending drugs, which is assisted suicide and goes against God's will.
The legislation passed on 11 September after a previous version failed this year despite the case of 29-year-old Brittany Maynard. The California woman with brain cancer moved to Oregon to end her life. Her mother Deborah Ziegler told NBC 7 she is committed more than ever to fight for an individual's right to die.
"You're not forcing anything on anyone. You're just giving us an option and we, like you, can say no, and we can say that doesn't fit my lifestyle," said Ziegler.
Maynard's family attended the legislative debate in California with her mother, Debbie Ziegler, testifying in committee hearings and carrying a picture of her daughter as she listened to lawmakers' debate.
In a video recorded days before Maynard took life-ending drugs, she told California lawmakers that no one should have to leave home to legally kill themselves under the care of a doctor, as reported by The Brandon Sun.
"No one should have to leave their home and community for peace of mind, to escape suffering, and to plan for a gentle death," Maynard said in the video released by right-to-die advocates after her death.
California will become the fifth state in the US to allow terminally ill patients to legally end their lives using doctor-prescribed drugs. It includes requirements that the patient be capable of taking the medication themselves and that two doctors approve it.
Governor Jerry Brown, a former Jesuit seminarian, announced on Monday 5 October that he signed a bill approved by state lawmakers after an emotional and deeply personal debate, according to AP.
California's measure came after at least 24 states introduced aid-in-dying legislation this year, though the measures stalled elsewhere. Doctors in Oregon, Washington, Vermont and Montana already can prescribe life-ending drugs.
The Catholic Church targeted Catholic lawmakers before the bill's passage and urged the governor to veto it. "Pope Francis invites all of us to create our good society by seeing through the eyes of those who are on the margins, those in need economically, physically, psychologically and socially," the California Catholic Conference said in a statement after its passage. "We ask the governor to veto this bill."