During a seven week trial the court heard the little boy, Joseph, was systematically abused in the two-months leading up to his death.
The court also heard the 42-year-old mother brutally murdered her then three-year-old because he looked like his biological father.
'This was a terrible crime of child murder,' Justice Peter Johnson said when sentencing the pair at the NSW Supreme Court in Darlinghurst today.
The jury were at times brought to tears as they heard evidence of how the toddler was held captive in ice-filled esky's, beaten with a wooden spoon, gagged with duct tape and had his head slammed in doors.
The boy’s stepfather was also charged with murder because he was part of a joint criminal enterprise with the mother to abuse and mistreat him.
During the trial the court heard from the deceased toddler’s older brother who told the jury about a time he heard the little boy screaming after being locked inside an ice-filled esky.
The brother also gave evidence about how he witnessed his little brother desperately trying to rip duct tape off his eyes on one occasion but the mother and stepfather kept sticking it back on.
Both the mother and stepfather maintained their innocence and pleaded not guilty to murder.
The pair have been jailed for a sentence of at least 33 years.