Kwame Adom Carpenter was found guilty of killing Moureen Gathua, 24, and their 6-month-old son Kyan Gathua-Carpenter in June 2015.
Video: Kwame Carpenter arrested in June 2015 in deaths of his wife, infant son
Father detained in connection to deaths of baby, child's mother in OC
Investigators said after an argument with his girlfriend, he stabbed her and their son with a kitchen knife and then fled the scene.
He was found and arrested the next day following a short police chase.
The initial charges were two felony counts of murder with special circumstances and a sentencing enhancement for personal use of a deadly weapon. He faces a minimum sentence of life in state prison without possibility of parole and could be eligible for the death penalty.
A sentencing hearing is set for April 26.