Three-year-old Joseph had his head slammed in a cupboard, eyes covered with duct tape and naked body shut in a freezing esky in the weeks before he died.
On Tuesday, the toddler's mother and stepfather, who have long claimed he was fatally tripped by a rope tied to the family's dogs, were found guilty of his 2014 murder in NSW.
"We got the right judgment," an emotional uncle told reporters after Justice Peter Johnson expressed his condolences to Joseph's extended family in court.
"(There's) no winners today. A little boy won't be coming back."
It took the jury two-and-a-half days of deliberating to convict the pair, who had assumed custody from Joseph's grandparents about seven weeks before he was found in cardiac arrest at the family's Oberon home.
His stepfather, 47, told police he taped a ball into the child's mouth and caused his penis to swell by flicking it with a wooden spoon.
The boy's 42-year-old mother, who cannot be named, had talked of "pummelling" his head in and killing him because he looked like his father, the trial heard.
"I did it and I want to die," the trial heard Joseph's mother say in a police-recorded conversation with her then-partner.
Joseph died in hospital three days after being treated by paramedics.
The crown alleged his mother likely inflicted the fatal injury but the stepfather was complicit because he must have known she could have and wanted to kill the boy.
Joseph's adult half-brother told the trial the boy started talking like a baby after moving in with his mother.
Duct tape was wrapped around the boy's eyes and head because the mother could not stand him staring at her, while on another occasion he was forced naked into an esky full of ice, the trial heard.
"I have never heard a person scream like that," said the half-brother, who recalled Joseph's stepfather holding the esky lid down for more than five minutes.
"I went outside because I couldn't take it any more."
The killers did not react as the verdicts were handed down.
They are due to face a sentence hearing on August 11.