The Riverside County jury found Michael Barbar, 55, guilty of two counts of first-degree murder in the deaths of Maysam Barbar and her daughter, Tamara.
Jurors also found true the special circumstance allegation of lying in wait, which makes Barbar eligible for the death penalty.
Barbar, who helped raise the child since birth, became suspicious about her paternity after discovering his wife had three separate affairs, prosecutors said.
He pulled Tamara out of school and swabbed her cheek for a DNA sample while eating at a McDonald's. When the paternity test showed the child was not his, Barbar spent eight days plotting the Nov. 14, 2009 murders, according to The Riverside Press-Enterprise.
Barbar first strangled his wife with a computer cord as she was handcuffed and naked on the floor, prosecutors said, then went to Tamara's room and tried to strangle her as she slept. When she struggled, Barbar bashed her head into the bedpost as many as 20 times, crushing her skull, prosecutors said.
Barbar was planning to kill his wife's lover in Texas and flee to Lebanon but was stopped by police in New Mexico after authorities tracked his cellphone signal, according to evidence at the trial.
Eric Keen, Barbar's defense attorney, said the killings were not planned but carried out in an uncontrollable rage. He asked jurors to find his client guilty of involuntary manslaughter.
Barbar's 13-year-old daughter Tarah testified that she heard her younger sister's cries and her father marching up and down the stairs carrying garbage bags as she lay in bed the night of the killings. The next morning, she found her sister's bed covered in blood and her mother's room locked, she said.
The penalty phase of trial begins July 30.