Peterson, 58, sat stoically looking straight ahead and did not react as the verdict was read. Several of his third wife's relatives gasped before hugging each other as they cried quietly in the courtroom.
Illinois has no death penalty, and Peterson now faces a maximum 60-year prison term when sentenced in Kathleen Savio's death on Nov. 26.
The trial was the first of its kind in Illinois history, with prosecutors building their case largely on hearsay thanks to a new law, dubbed "Drew's Law," tailored to Peterson's case. That hearsay, prosecutors had said, would let his third and fourth wives "speak from their graves" through family and friends to convict Peterson.
Hearsay is any information reported by a witness that is not based on the witness' direct knowledge. Its use at the trial could also be grounds for an appeal from Peterson.
The verdict is a vindication for Will County State's Attorney James Glasgow and his team, who gambled by putting on a case that they themselves conceded was filled with holes. They then went on to commit a series of blunders during testimony that drew the judge's ire.
One question at trial was how much Peterson's personality might influence the jurors. Before his 2009 arrest, the glib, cocky Peterson seemed to taunt authorities, joking on talk shows and even suggesting a "Win a Date With Drew" contest. His notoriety inspired a TV movie starring Rob Lowe.
It all began with a gruesome discovery.
A neighbor came across Savio's body on March 1, 2004, and let out a scream. Others ran up the stairs of her suburban Chicago home to behold the scene: Savio lay face down in her dry bathtub. Her thick black hair was blood-soaked and she had a 2-inch gash on the back of her head.
The drowning death of the 40-year-old aspiring nurse was initially deemed an accident -- a freak slip in the tub. After Peterson's fourth wife, 23-year-old Stacy Peterson, went missing in 2007 Savio's body was exhumed, re-examined and her death reclassified as a homicide.
Peterson had divorced Savio a year before her death. His motive for killing her, prosecutors said, was fear that a pending settlement, which included their $300,000 home, would wipe him out financially.
The 12 jurors, who raised questions about whether they were taking the case seriously by donning different coordinated outfits each day of testimony, deliberated for more than 13 hours before reaching a decision. The seven men and five women included a poet, a letter carrier and a man who said his favorite TV show was "Criminal Minds."
Fascination nationwide with the former Bolingbrook police sergeant arose from speculation he sought to parlay three decades of law enforcement expertise into getting away with murder.
Kathleen Savio's brother, Nick Savio, grew emotional as he read a statement from the Savio family outside court, calling Drew Peterson a "cold-blooded killer" and saying "everyone gets payback for what they have done to others.
"Stacy, you are now next for justice," Nick Savio declared as he finished speaking.
Prosecutors suspect Peterson killed his pretty, sandy-haired fourth wife because she could finger him for Savio's death, but her body has never been found and no charges have ever been filed. Jurors weren't supposed to link her disappearance to Savio's death, and prosecutors were prohibited from mentioning the subject.
Stacy Peterson's family hoped a conviction in Savio's murder could lead to charges against Drew Peterson in Stacy's disappearance. He says his fourth wife ran off with another man and is still alive.
In trying Peterson for Savio's death, prosecutors faced enormous hurldes.
They had no physical evidence tying Peterson to Savio's death and no witnesses placing him at the scene. They were forced to rely on typically barred hearsay -- statements Savio made to others before she died and that Stacy Peterson made before she vanished. Illinois passed the hearsay law in 2008, making the evidence admissible at trials in rare circumstances.
The hearsay included friend Kristin Anderson testifying that Savio told her Peterson once warned her at knife point, "I could kill you and make it look like an accident."
Stacy Peterson's pastor, Neil Schori, testified she told him that her husband got up from bed and left their house in the middle of the night around the time of Savio's death. Drew Peterson later coached his fourth wife on how to lie to police, Schori said.
There was some damning testimony not based on hearsay.
A former co-worker of Peterson's, Jeff Pachter, testified that Peterson offered him $25,000 to hire a hit man to kill Savio, though he never followed through. After Savio was found dead, Peterson told him, "That favor I asked you -- I don't need it anymore."
Prosecutors had to establish the most basic fact for a murder trial: that there was actually a murder. Pathologists testified for the defense that Savio's wounds indicated an accident; those testifying for the state said it was impossible for a single fall to cause both the wound on the back of her head and the bruises on the front of her body.
Peterson's lawyers endeavored to cast doubt on the reliability of key witnesses. They accused Savio's sister, Susan Doman, of jazzing up her testimony to profit from a movie and book deal.
Peterson's band of colorful, wisecracking defense attorneys -- who joked outside court that Stacy Peterson could show up any day to take the stand -- committed their own share of errors.
As they sought to blunt the credibility of hearsay, for instance, they ended up prompting one of their own witnesses to repeatedly emphasize that Stacy Peterson was convinced her husband did kill Savio.
Peterson could still win release someday. His attorneys have said they may appeal all the way to the U.S. Supreme Court on grounds Illinois' hearsay law is unconstitutional.
Some legal experts worried about the precedent a conviction dependent on hearsay would set, saying it could open the floodgates for the admissibility of such evidence in Illinois and elsewhere.