His little boy Cooper Harris was found dead on June 18 2014, after spending around seven hours strapped in a rear-facing child seat in his dad's SUV. He died of hypothermia after temperatures outside reached 32 degrees.
Harris was meant to take Cooper to daycare on his way to work as a web developer, but instead left him in his work car park for an entire day. After 'discovering' Cooper's lifeless body on his way to see a movie, Harris called the police saying he'd forgotten to drop his child at daycare.
After what initially seemed like a tragic accident, police then found evidence of Harris' extra-marital affairs and suspicions turned to him. They discovered that on the day of Cooper's death, Harris had been exchanging sexual messages with six other women, including a prostitute some who were underage.
Police concluded that Harris had killed Cooper on purpose so that he could be free to lave his wife, Leanna Harris.
During the trial, the defence team argued that Harris was a loving father and that while he was responsible for the boy's death, it was a tragic accident.
However, prosecutors said Harris had known Cooper was in the car.
'He thought he was smarter than anybody else. He didn't think anyone was going to call his bluff and get away with it,' said lead prosecutor Chuck Boring.
They also pointed to evidence that Harris had gone for a chicken meal and bought light bulbs on his lunch break. Afterwards he'd gone to his car to put the bulbs inside, still not noticing his son was inside.
His wife Leanna supported Harris through the trial, saying he would never intentionally kill their baby and his extra-marital affairs were a separate issue to their boy's death.
After he was found guilty, Leanna told ABC News that their son's death was a tragic accident.
'There was evidence in our relationship that would suggest that he would be capable of being unfaithful to me,' she said. 'There was no evidence in our relationship that suggested that he would harm anyone, much less his own son.'
Leanne divorced Harris in March 2016 and went back to using her maiden name of Taylor.
According to The Atlanta Journal-Constitution, Justin Ross Harris is currently in solitary confinement for his own safety at Macon State Prison and has filed a motion for a new trial.