Peterson, 58, sat stoically looking straight ahead and did not react as the judge announced jurors had found him guilty of first-degree murder in the death of his third wife, Kathleen Savio. Her relatives gasped, then hugged each other as they cried quietly.
Illinois has no death penalty, and Peterson now faces a maximum 60-year prison term when sentenced 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. Defense attorneys said its use at the trial would be central to their appeal.
Savio's family members were emotional as they left the courtroom. Her sister, Susan Dorman, threw herself into the arms of her husband, Mitch Dorman.
"Finally, finally, finally. ... We finally got that murdering bastard," Savio's brother-in-law, Mitch Dorman, said.
Peterson's personality loomed over the trial, and bystanders gathered outside the courthouse began chanting, "Loser. Loser. Loser," as reporters interviewed his attorneys. 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.
"The whole world has been waiting for Drew Peterson to be convicted. They hate him. ... They passed a law to get this individual," said defense attorney Joe Lopez.
The verdict was a vindication for Will County State's Attorney James Glasgow and his team, who gambled by putting on a case they conceded was filled with holes.
Glasgow drew cheers from the crowd gathered outside the courthouse.
"He was a thug," Glasgow said of Peterson. "He would threaten people because he had a gun and a badge. Nobody would take him on, but we took him on and he lost."
A neighbor came across Savio's body on March 1, 2004. She was face down her dry bathtub, her thick, black hair soaked in blood and a 2-inch gash was 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, vanished in 2007, Savio's body was exhumed, re-examined and her death reclassified as a homicide.
Drew 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 deliberated for more than 13 hours before reaching a decision. The seven men and five women raised questions about whether they were taking the case seriously by donning different coordinated outfits each day of testimony, but did not wear matching attire Thursday.
Jurors didn't talk to reporters after the verdict. They issued a brief statement saying they believe their decision was just.
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.
Savio's brother, Nick Savio, grew emotional as he read a statement from the 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 said they hoped the conviction will lead to a break in Stacy's case. He says his fourth wife ran off with another man and is still alive.
Prosecutors faced enormous hurdles as they tried Peterson for Savio's death.
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 knifepoint, "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.
Peterson's attorneys have said they may appeal all the way to the U.S. Supreme Court on grounds Illinois' hearsay law is unconstitutional.
"It's a very dark day in American when you convict someone on hearsay evidence," Lopez said.
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.
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 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 their own witness to repeatedly emphasize that Stacy Peterson was convinced her husband killed Savio.