Gavin Newsom is to sign an executive order placing a moratorium on executions, as well as withdrawing the lethal injection regulations that death penalty opponents have tied up in court.
There are 737 people on death row in California.
Prepared remarks by the Californian governor read: "The intentional killing of another person is wrong and as governor, I will not oversee the execution of any individual.
"I do not believe that a civilised society can claim to be a leader in the world as long as its government continues to sanction the premeditated and discriminatory execution of its people."
Mr Newsom said the death penalty is "a failure" that "has discriminated against defendants who are mentally ill, black and brown, or can't afford expensive legal representation".
And he said innocent people have been wrongly convicted and sometimes put to death.
No one has been executed in California since 2006, when Arnold Schwarzenegger was governor.
In 2016, voters narrowly approved a ballot measure to speed up punishment, but no one faced imminent execution.
Since the last execution, the state's death row has grown, and now accounts for one in four of total condemned inmates in the US.
On California's death row is Scott Peterson, who killed his pregnant wife Laci, and Richard Davis, who kidnapped and strangled 12-year-old Polly Klaas while she was at a sleepover.
Michele Hanisee, president of the Association of Deputy (Los Angeles County) District Attorneys, said Mr Newsom was "usurping the express will of California voters and substituting his personal preferences via this hasty and ill-considered moratorium on the death penalty".
Mr Newsom does not have the power to overturn California's death penalty law, but he can refuse to sign any death warrants, and can change death sentences to life in prison.
The move is likely to be challenged in court.
In two other US states where the governor enacted a moratorium, Washington and Illinois, executions were eventually outlawed.
Mr Newsom said the death penalty was not a deterrent, wasted taxpayer money and is flawed because it is "irreversible and irreparable in the event of human error".
Since 1973, five California inmates who were sentenced to death were later exonerated.
Now, more than 60% of condemned inmates in California are minorities, which Mr Newsom's office says proves there is a racial disparity in who is sentenced to death.
Last April, Vicente Figueroa Benavides was freed in California after spending 25 years on death row for the murder of a young girl. A court ruled a testimony given at his trial was false.