Bulger, 83, stood silently and showed no reaction to verdict, which brought to a close a case that not only transfixed the city with its grisly violence but exposed corruption inside the Boston FBI and an overly cozy relationship between the bureau and its underworld snitches.
Bulger was charged primarily with racketeering, which listed 33 criminal acts - among them, 19 murders that he allegedly helped orchestrate or carried out himself during the 1970s and '80s while he led the Winter Hill Gang, Boston's ruthless Irish mob.
After 4½ days of deliberations, the federal jury decided he took part in 11 of those murders, along with nearly all the other crimes on the list, including acts of extortion, money-laundering and drug dealing. He was also found guilty of 30 other offenses, including possession of machine guns.
Bulger could get life in prison at sentencing Nov. 13. But given his age, even a modest term could amount to a life sentence for the slightly stooped, white-bearded Bulger.
As court broke up, Bulger turned to his relatives and gave them a thumbs-up. A woman in the gallery taunted him as he was led away, apparently imitating machine-gun fire as she yelled: "Rat-a-tat-tat, Whitey!"
Outside the courtroom, relatives of the victims hugged each other, the prosecutors and even defense attorneys.
Patricia Donahue wept, saying it was a relief to see Bulger convicted in the murder of her husband, Michael Donahue, who authorities say was an innocent victim who died in a hail of gunfire while giving a ride to an FBI informant marked for death by Bulger.
"He's guilty of murdering my husband. There's nobody that said that," his widow said.
Thomas Donahue, who was 8 when his father was killed, said: "Thirty-one years of deceit, of cover-up of my father's murder. Finally we have somebody guilty of it. Thirty-one years - that's a long time." He said that when he heard the verdict, "I wanted to jump up. I was like, 'Damn right.'"
"Today is a day that many in this city thought would never come," said U.S. Attorney Carmen Ortiz. "This day of reckoning has been a long time in coming." She added: "We hope that we stand here today to mark the end of an era that was very ugly in Boston's history."
She said Bulger's corrupting of law enforcement officials "allowed him to operate a violent organization in this town, and it also allowed him to slip away when honest law enforcement was closing in."
Bulger attorney J.W. Carney Jr. said Bulger intends to appeal because the judge didn't let him argue that he had been granted immunity for his crimes by a now-dead federal prosecutor.
But Carney said Bulger was pleased with the trial and its outcome, because "it was important to him that the government corruption be exposed, and important to him to see the deals the government was able to make with certain people."
"Mr. Bulger knew as soon as he was arrested that he was going to die behind the walls of a prison or on a gurney and injected with chemicals that would kill him," Carney said. "This trial has never been about Jim Bulger being set free."
Bulger, the model for Jack Nicholson's sinister crime boss in the 2006 Martin Scorsese movie "The Departed," was seen for years as a Robin Hood figure who bought Thanksgiving turkeys for fellow residents of working-class South Boston and kept hard drugs out of the neighborhood. But that image was shattered when authorities started digging up bodies.
Prosecutors at the two-month trial portrayed Bulger as a cold-blooded, hands-on boss who killed anyone he saw as a threat, along with innocent people who happened to get in the way. Then, according to testimony, he would go off and take a nap while his underlings cleaned up.
Among other things, Bulger was accused of strangling two women with his bare hands, shooting two men in the head after chaining them to chairs and interrogating them for hours, and opening fire on two men as they left a South Boston restaurant.
Bulger skipped town in 1994 after being tipped off - by a retired FBI agent, John Connolly, it turned out - that he was about to be indicted.
He spent 16 years on the run and was on the FBI's 10 Most Wanted list before he was finally captured in 2011 in Santa Monica, Calif., where he had been living in a rent-controlled apartment near the beach with his longtime girlfriend, Catherine Greig. She was sentenced to eight years in prison for helping Bulger.
His disappearance proved a major embarrassment to the FBI when it came out at court hearings and trials that Bulger had been an informant from 1975 to 1990, feeding the bureau information on the rival New England Mafia and members of his own gang while he continued to kill and intimidate.
Those proceedings also revealed that Bulger and his gang paid off several FBI agents and state and Boston police officers, dispensing Christmas envelopes of cash and cases of fine wine to get information on search warrants, wiretaps and investigations and stay one step ahead of the law.
At his trial, Bulger's lawyers tried to turn the tables on the government, detailing the corruption and accusing prosecutors of offering unconscionably generous deals to three former Bulger loyalists to testify against him.
The defense portrayed the three key witnesses - gangster Stephen The Rifleman" Flemmi, hit man John Martorano and Bulger protege Kevin Weeks - as pathological liars who pinned their own crimes on Bulger so they could get reduced sentences.
But overall, the defense barely contested many of the charges against Bulger. In fact, his lawyers conceded he ran a criminal enterprise that took in millions through drugs, gambling and loansharking.
His lawyers did strongly deny he killed women, something Bulger evidently regarded as a violation of his underworld code of honor. The jury ultimately found he had a role in the strangling of one woman - Flemmi's stepdaughter - but it could not reach a decision on the other woman, Flemmi's girlfriend.
Prosecutors said the women were killed because they knew too much about the gang's business.
The defense also spent a surprising amount of time disputing he was a "rat" - a label that seemed to set off the hotheaded Bulger more than anything else, causing him to erupt in obscenities in the courtroom.
Bulger's lawyers argued that Connolly, Bulger's supposed handler inside the FBI, fabricated Bulger's thick informant file to cover up his corrupt relationship with the gangster and advance his own career.
The prosecution's witnesses also included drug dealers, bookmakers and legitimate businessmen who described terrifying encounters with Bulger in which he ordered them to pay up or take a beating or worse.
Real estate developer Richard Buccheri said Bulger threatened to kill him and his family if he did not pay $200,000. Buccheri related how Bulger slammed his hand on a table in anger.
"With that, he takes the shotgun that was on the table - he sticks it in my mouth," Buccheri said as spectators in the courtroom gasped.
Before the trial, Bulger's lawyers said he would take the stand and detail graft inside the FBI. But after Judge Denise Casper disallowed his claim of immunity, Bulger did not testify.
"As far as I'm concerned, I didn't get a fair trial, and this is a sham, and do what youse want with me," he complained to the judge as the trial wound down. "That's it. That's my final word."
Bulger's life story fascinated Bostonians for decades. He grew up in a South Boston housing project and quickly became involved in crime, while his brother William rose to become one of the most powerful politicians in Massachusetts as state Senate president.
William Bulger was forced to resign as president of the University of Massachusetts system in 2003 after it was learned that he got a call from his brother while he was on the run and didn't urge him to surrender.