California Governor Gavin Newsom will announce a moratorium on executions and a temporary reprieve to all 737 inmates on death row in the state.
US media report he plans to sign an executive order later on Wednesday, describing the death penalty as “inconsistent with our bedrock values”.
California has not carried out any executions since 2006, as a series of court battles over execution methods have continued.
No death row inmates will be released.
Governor Newsom took office in January and a death penalty moratorium was one of his campaign pledges.
More than 900 people have been sentenced to death in California since 1978 but only 13 have been executed.
Another 79 have died of natural causes, and a further 26 committed suicide, figures from the California Department of Corrections and Rehabilitation show.