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
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.