California‘s governor is set to sign an executive order temporarily halting the state’s death penalty, granting reprieve to all 737 inmates on death row.

Gavin Newsom is also closing the state’s new execution chamber at San Quentin State Prison that has never been used.

“The intentional killing of another person is wrong and as governor, I will not oversee the execution of any individual,” he is expected to say on Wednesday, according to his office.

Mr Newsom will call the death penalty “a failure” that ”has discriminated against defendants who are mentally ill, black and brown, or can’t afford expensive legal representation”.

He will also say innocent people have been wrongly convicted and sometimes put to death. Mr Newsom is expected to sign the executive order on Wednesday.

Death row in California's San Quentin prison Show all 8 1 /8 Death row in California's San Quentin prison Death row in California's San Quentin prison A condemned inmate exercises in a cage out in the yard of San Quentin prison Getty Death row in California's San Quentin prison San Quentin State Prison opened in 1852 and is California's oldest penitentiary. The facility houses the state's only death row for men that currently has 700 condemned inmates Getty Death row in California's San Quentin prison The lethal injection facility at San Quentin prison AP Death row in California's San Quentin prison A condemned inmate stands in a cell out in the yard of San Quentin prison Getty Death row in California's San Quentin prison An armrest in the interior of the lethal injection facility at San Quentin prison AP Death row in California's San Quentin prison A cell on death row in San Quentin Getty Death row in California's San Quentin prison A cage on death row in San Quentin Getty Death row in California's San Quentin prison A cell on death row in San Quentin Getty

California’s death row is crowded with inmates as it hasn’t executed anyone since 2006, when Arnold Schwarzenegger was governor.

Since its last execution, its death row population has grown to house one in every four condemned inmates in the US.

Those on death row include Scott Peterson, whose trial for killing his wife Laci riveted the US, and Richard Davis, who kidnapped 12-year-old Polly Klaas during a sleepover and strangled her to death.

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,” said Michele Hanisee, president of the Association of Deputy (Los Angeles County) District Attorneys.

But Alison Parker, US managing director at Human Rights Watch, praised Mr Newsom’s “great courage and leadership in ending the cruel, costly, and unfair practice of executing prisoners,” and called for other states to follow California’s lead. The American Civil Liberties Union called it “a watershed moment in the fight for racial equity and equal justice for all.”

The American Civil Liberties Union called it “a watershed moment in the fight for racial equity and equal justice for all.”

António Guterres remarks at panel on transparency and the death penalty

Mr Newsom argued that the death penalty isn’t a deterrent, wastes taxpayer money and is flawed because it is “irreversible and irreparable in the event of human error.”

It is also costly, with California spending $5bn (£3.8bn) since 1978 on its death row, he said.

More than six in 10 condemned California inmates are minorities, which Mr Newsom’s office cited as proof of racial disparities in who is sentenced to die. Since 1973, five California inmates who were sentenced to death were later exonerated, his office added.