The move to halt executions was also panned by President Trump, who has been a harsh critic of Newsom's ever since the governor took office earlier this year.
Gavin Newsom is expected to sign an executive order on the death penalty on Wednesday morning.
"Friends and families of the always forgotten VICTIMS are not thrilled, and neither am I!" he tweeted Wednesday. Trump has cultivated an image of himself as a tough-on-crime president and has said drug dealers should face the ultimate penalty.
Newsom says the death penalty system has discriminated against mentally ill defendants and people of color.
California has executed 13 people since the U.S. Supreme Court reinstated the death penalty in 1976. "It has provided no public safety benefit or value as a deterrent".
"I couldn't sleep at night", he said at the state capitol.
Newsom's plan and Trump's response both reflect that split.
A court-ordered moratorium on executions has been in place since February 2006, when a federal judge declared that California's lethal injection protocol was unconstitutional.
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Execution chamber at the San Quentin prison. At the same time, a poll from PPIC found that most Californians preferred life imprisonment to the use of the death penalty. Twenty-four people now on California's death row were convicted of murder and have exhausted all of their appeals, the Times reported. It has wasted billions of taxpayer dollars.
Trump, of course, infamously called for the teenagers convicted in the Central Park Five jogging case to be executed, buying full page ads in NY newspapers demanding the state to bring back the death penalty.
Newsom said he had anticipated that within a month he would have been asked to sign off on a new protocol for administering lethal injections to death row inmates, clearing the way for executions to begin again. Voters that year also favored fast-tracking the appeals process, speeding up convicted killers' time on death row, through approving Proposition 66.
The 737 people on death row in California are the most of any state in America, the governor's office said.
The governor's decision brings California in line with Colorado, Oregon, and Pennsylvania - all of which have governor-issued moratoria - and adds momentum to a national movement working to end capital punishment.
"There is a lot of literature and studies out there that show that the death penalty is a deeply broken system for a lot of different reasons", the American Civil Liberties Union staff attorney Shilpi Agarwal said.
"But most of all, the death penalty is absolute, irreversible and irreparable in the event of human error", he continued.