Eko Hot Blog reports that With less than a month left in office, she said she was using her executive power because she believed capital punishment was wrong.
Oregon is one of 27 states that allow the death penalty, but it has not executed a prisoner since 1997.
Republicans in the western US state condemned Ms Brown’s order.
It will take effect on Wednesday.
In a statement, she said she was not acting because these prisoners had been rehabilitated, but because the death penalty is “immoral”.
“It is an irreversible punishment that does not allow for correction; is wasteful of taxpayer dollars; does not make communities safer; and cannot be and never has been administered fairly and equitably,” she said.
Ms Brown has used her clemency powers more than any other previous Oregon governor.
According to her office, she is the seventh US governor in the past 50 years to commute all death sentences in a state.
Oregon State Senate Leader Tim Knopp, a Republican, assailed her policy on Tuesday.
“Did the people of Oregon vote to end the death penalty?” he said. “I don’t recall that happening.”
He added: “Even in the final days of her term, Brown continues to disrespect victims of the most violent crimes.”
Capital punishment is written in Oregon’s constitution, meaning another governor can choose to resume the practice in the future.
The Democrat replacing Ms Brown, Tina Kotek, has said she opposes the death penalty because of her religious beliefs.
Seventeen people have been executed in the US in 2022, according to the Death Penalty Information Center.
An opinion poll from earlier this year found Ms Brown to have the lowest approval rating of any US governor.
Source: BBC
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