The jury convicted Brancato of a lesser charge of attempted burglary. He faces a minimum of three years in prison on that count, but the former actor could get credit for time served because he has been behind bars about that long.
Brancato showed no reaction as the verdict was read - his face impassive, his fingers pressed together. His mother, seated a couple rows back in the gallery, began sobbing.
Prosecutors say Brancato and accomplice Steven Armento broke into a basement apartment to steal prescription drugs after a night of drinking at a strip club. Officer Daniel Enchautegui, who lived next door, came out to investigate.
Armento blasted the 28-year-old officer with his .357 Magnum, hitting him in the heart. The dying officer fired back, wounding both men. Armento was convicted earlier this year of first-degree murder and was sentenced to life in prison without parole.
Yolanda Rosa Nazario, the victim's sister, said she was baffled by the verdict.
"What message is this sending out to the New York City police officers today? It's wrong," she said.
"This would not have happened if not for this animal's drug habit," said Patrolmen's Benevolent Association head Patrick Lynch. "The only good thing is that this skunk is not walking out to spend Christmas with his family. The sad part is that neither is Daniel."
Brancato was led out of court in handcuffs. The next hearing is scheduled for Jan. 9.
Defense lawyer Joseph Tacopina said his client was relieved with the verdict. "There was never going to be smiles," he said. "This is not a case that warrants that."
Tacopina added: "This will be a second chance for him in life. ... Lillo's committed to taking advantage of it."
Brancato rose to fame in the 1993 movie "A Bronx Tale," playing a young kid from the neighborhood who is torn between two worlds and two men: a local mobster played by Chazz Palminteri and his straight-and-narrow bus-driver father, played by Robert De Niro.
Other roles followed, most notably a stint on the second season of "The Sopranos." His character carried out a series of low-level crimes for the New Jersey mob before being gunned down by Tony Soprano and his sidekick as he tearfully begged for his life.
Brancato, 32, and Armento, 48, were drinking together at a strip club in December 2005 before deciding to break into the basement apartment in a hunt for Valium, prosecutors said.
Brancato testified during the trial there was a never a break-in. He claimed that he had known the owner, a Vietnam veteran, for several years. He also said he had permission to go inside and take painkillers and other pills whenever he felt like it, and didn't know the man had died earlier that year.
The pills were part of a drug problem that he said began when he was "introduced to marijuana" on the set of "A Bronx Tale." He later became hooked on crack and heroin, he said.
He told the jury that while suffering from judgment-impairing heroin withdrawals on the night of the shooting, he accidentally broke the kitchen window of the apartment in a desperate attempt to wake up his old pill-supplier.
"I was becoming dope sick," Brancato testified. "Mentally, I was a mess."
Brancato tried to deflect suggestions by the prosecution that his testimony - at times punctuated by vignettes about his drug-crazed downfall - was another acting job.