The jury also found Peterson guilty of the second-degree murder of their unborn child.
Peterson, 32, was charged with killing Laci Peterson, who was eight months pregnant.
The decaying bodies of her and her baby washed ashore in April 2003 along an area of the San Francisco Bay where Peterson said he was fishing the day Laci disappeared from their home in Modesto, California.
Peterson showed little reaction as the verdict was read, although his mother, Jackie, appeared numb with shock. Hundreds of people gathered outside the court to await the verdict, some of whom cheered upon hearing the verdict.
Prosecutors said Peterson pretended to be concerned about his missing wife when he was more interested in his mistress, Amber Frey, and staying free of family obligations.
Defence lawyer, Mark Geragos, said that Peterson was framed and that prosecutors provided no evidence or motive to connect him with the murders.
The judge ordered the two sides and the jury to refrain from speaking about the case before the penalty phase of the trial begins on November 22. The jury is expected to decide, starting on November 30, whether to impose the death penalty or life without parole.
Even if he receives the death penalty, Peterson could be alive for a long time. California has averaged more than 20 years from the time of sentencing to the time of execution.
The verdict came after two jurors were unexpectedly removed from the sequestered jury in recent days and then replaced by alternates, forcing the second resumption of deliberations.
The case attracted wide media coverage, as many were taken by the story of a good-looking, white, all-American couple struck by tragedy. Photographs of a smiling Laci made the saga natural fodder for cable television.
According to the US Department of Justice, about a third of female murder victims in recent years have been killed by their spouses or others with whom they are intimate. According to the FBI, spouses killed their partners on 804 occasions in 2002 – the year of Laci Peterson’s death.