Investigators say they found the 44-year-old Luis Romero dead in his cell during a routine security check Saturday morning.
Officers have detained the victim's cellmate, 31-year-old Jaime Osuna, as the suspected killer. Osuna has been placed in an administrative segregation unit.
Officials say Osuna was received by the prison in 2017 serving a life sentence for the 2011 killing and torture of a Bakersfield woman.
The prison's Investigative Services Unit and the Kings County Sheriff's Office have launched an investigation.
Officials say Romero was serving a life sentence with a chance at parole for second-degree murder.