Just hours before leaving office in January, Schwarzenegger commuted the voluntary manslaughter sentence of Esteban Nunez from 16 years to seven. Nunez is the son of former California Assembly speaker Fabian Nunez, a Schwarzenegger ally when both were in office.
Schwarzenegger did not notify prosecutors or the victim's family beforehand.
On Monday, Brown said he had signed AB648 by Democratic Assemblyman Marty Block of San Diego. It requires the governor to give at least 10 days' notice to the district attorney in the jurisdiction where the crime occurred before acting on an application for clemency.
Such a move would give the district attorney time to notify crime victims and allow them to petition against a sentence reduction.
Luis Santos, 22, was fatally stabbed in an altercation involving Esteban Nunez near San Diego State University three years ago Tuesday.
Santos's family and San Diego prosecutors hailed the new law.
"At least no other family will have to deal with the travesty of having courtroom justice taken away due to secretive backroom conniving moves," said Kathy Santos, Luis's mother.
The Associated Press contributed to this report.