A man who left his toddler son to die in a hot car over a period of seven hours has been sentenced to life in prison without parole.

Justin Ross Harris, 36, was convicted of malice murder and other offences last month when a jury found him guilty of intentionally leaving his 22-month-old son Cooper in his SUV to die.

Harris’ child died in June 2014 in Georgia after he was left in the car while his father went to his job as a web developer for Home Depot. Harris had driven himself and Cooper to a Chick-fil-A restaurant for breakfast before driving to work. He told police he forgot to take Cooper to day care and that he left him strapped into his seat in the car without realising.

Cooper was in the car for seven hours on a day when temperatures reached the high 80s in Fahrenheit and died of hypothermia.

Police later discovered that Harris, who was married at the time, had been having both online and offline relationships with a number of women, including a prostitute and a teenager, and prosecutors argued that he had intentionally killed his son to escape his family life.

Harris’ defence attorneys said throughout the trial that he was a loving father who had had no intention of killing his son, calling Cooper’s death a tragic accident.

Harris was convicted of malice murder, child cruelty and sex crimes relating to the text messages sent to the teenage girl. In addition to the life term for the murder charge, Harris was given an additional 23 years for the other crimes.

Cooper Harris who died after being left in his father's car. (Facebook)

Harris, who was wearing an orange prison jumpsuit with his hands and ankles shackled, declined to speak at the sentencing. He frowned throughout the proceeding but did not show any emotion as the sentence was read out.

Cobb County Superior Court Judge Mary Staley Clark told Harris she thought about statements he had made during conversations with police and his wife on the day his son died about wishing to be an advocate to keep anyone else from ever leaving a child in a hot vehicle.

“Perhaps, not in the way you intended, you have accomplished that goal,” she said during the sentencing.

Cobb County Senior Assistant District Attorney Chuck Boring, the lead prosecutor on the case, told reporters after the hearing: “I don’t think you could have any other sentence that would be appropriate when somebody’s been convicted of intentionally taking the life of a 22-month-old – not only doing that but doing it in such a painful and deliberate way.”