Jurors took three hours to reach the verdict, meaning that they accepted April Jace's killing was not premeditated but believed it to be more serious than voluntary manslaughter.
The 53-year-old actor, famous for his role in The Shield has to face up to 40 years in jail when he is sentenced on June 10.
Deputy district attorney Tannaz Mokayef told jurors in her summing up on Friday that Mr Jace was "obsessed" with his wife, who had been trying to leave him amid his allegations that she had been unfaithful.
Mr Jace's defence team accepted that he had shot his wife in the back and twice in her legs on May 19, 2014, but maintained that he was guilty only of voluntary manslaughter, sometimes called a "crime of passion."
"He snapped. If you find there was something that provoked this man and it created some kind of passion in him, that's manslaughter," his attorney Jamon Hicks told jurors.
The couple's 10-year-old son Nehemiah, testified that he had seen his father bring his mother - a keep fit enthusiast into the hallway of their home in the Hyde Park area, where she fell down.
"Then my dad said, 'If you like running, run to heaven,' and then he shot her," the boy told the jury.
In a recorded interview played in court, Mr Jace told police that he was holding the gun when his wife returned home from a baseball game with their sons.
She lunged at him, he said, and he had intended "just to shoot her in the leg" and not kill her, adding that he had been drinking.
The couple had exchanged 164 text messages on the day of the shooting, the court was told, including one in which Mr Jace's wife of nine years said she was "afraid to come home."
The actor, who split from his previous wife, Jennifer Bitterman, in 2002, filed for bankruptcy in 2011, citing debts of more than $500,000. Neighbours reported that he had struggled to find work since the end of The Shield.
In addition to Forrest Gump, Mr Jace appeared in Boogie Nights and Planet of the Apes.