The jury took just over five hours, split with an overnight break, to find Gosnell, 28, guilty of murder in a unanimous decision.Gosnell admitted killing 15-year-old Hayden after a savage, prolonged assault at his Cashel St flat on August 22, 2011.
He then sawed the schoolboy into 12 pieces with a $20 jigsaw and dumped his remains in two city graveyards, and his organs were buried in the backyard.
But he denied murderous intent, and has asked to be convicted of manslaughter.
Gosnell has previously pleaded guilty to a charge of offering an indignity to a human a body.
In a harrowing trial, which was halted on Friday after a jury began sobbing over grisly dismemberment evidence, Gosnell admitted the teen died at his hands.
The court heard how Gosnell snapped when Hayden told him his then girlfriend, Nicolette Vaux-Phillips, was using him, and didn't like him.
Defence counsel Craig Ruane said it was a brutal assault that "went too far''.
The jury heard from Vaux-Phillips - who witnessed the attack and was last year sentenced to 12 months of home detention after admitting being an accessory after the fact to culpable homicide - as well as from Hayden's mother, Jacqueline Miles, police officers, forensic experts, and friends of Gosnell who saw the dead teen's body the next day.
Forensic pathologist Dr Martin Sage said Hayden probably died of brain injuries but his decomposed body parts meant it was impossible to definitively rule his exact cause of death.
After closing arguments by the Crown and defence this morning, Justice Lester Chisholm summed up early this afternoon.
Crown prosecutor Barnaby Hawes said the only rational conclusion is murder.
Gosnell's attitude changed during the prolonged attack, he said, and the force of his punches and kicks became "harder and harder''.
He also highlighted the fact Gosnell said he was trying to knock out Hayden, while laughing during the bashing, when the teen was begging for it to stop, crying, and trying to get away.
Mr Ruane said there was no premeditation before the assault occurred.
The fact Gosnell was shaken up and panicked the next morning when he saw Hayden dead on his couch, meant he didn't mean to kill him, Mr Ruane said.
Justice Chisholm said issues in the trial were relatively narrow, coming down to whether it was a case of murder or manslaughter.
Hayden's father's family were delighted with the verdict.
"The family are pleased with the verdict that the jury has arrived at today.
"We sincerely thank all of those who have been involved in this case and all those who have offered us support throughout this ordeal.
"We will always miss Hayden and grieve the fact that his life was taken so early.
"We will never come to terms with the extreme violence and cruelty that Hayden suffered at Gavin's hands, nor the extreme disrespect he showed in dismembering and concealing his body.
"We would also like to publicly condemn all those who knew what had happened to Hayden but did not come forward at the earliest opportunity. Through their inaction they condoned Gavin's heinous behaviour.
"Gavin Gosnell preyed upon a vulnerable member of society. His actions following the murder were based on self-preservation rather than any sense of remorse or empathy.
"Society needs to be protected from such a callous and inhumane individual.
"Gavin should be sentenced to the full extent of the law. Hayden was just a boy.''
Mr Ruane said he'd spoken to his client after the verdict but declined to comment as he left court
Miles' friends and family in the public gallery gasped, clapped and sobbed 'Yes', when the guilty verdict was read out.Gosnell, as he had throughout the trial kept his head bowed low in the dock.He was led into custody without looking up.
Outside court, Hayden's aunty Sandy Ward read out a statement that spoke of the family's relief that the trial was over and Gosnell had been found guilty of murder.
The family also thanked the jury for its decision, knowing that the trial would have been "emotionally very difficult''.
"We hope that the sentence that will be given to Gavin Gosnell reflects the seriousness of his crime,'' she said."This last 17 months have been horrific for our family and we find it incredibly hard to put in words how this has affected us.''
She also thanked the police team for its investigations, support and guidance, as well as friends, family, and community for "incredible generosity, love and support'' which they have found "overwhelming and humbling''.
The family said they wanted to remember Hayden as the "gentle, caring, funny, and creative young boy", and not what happened to him "on that horrific night''.
"He loved his family and his family loved him very much. We miss him every day,'' she said.
His mum, Jacqueline Miles, supported by Mrs Ward, said she loved her son so much, and that he was "in my heart''.
