An Adelaide man who killed another motorist during an extreme episode of road rage will spend at least 20 years behind bars.

Key points: Benjamin Joshua George pleaded guilty to murder earlier this year

Benjamin Joshua George pleaded guilty to murder earlier this year The court heard his victim, Troy McLean died after being stabbed

The court heard his victim, Troy McLean died after being stabbed George will spend at least 20 years behind bars

Benjamin Joshua George, 27, pleaded guilty earlier this year to murdering 34-year-old Troy James McLean at Salisbury in 2017.

The Supreme Court previously heard Mr McLean accidentally nudged the back of George's Car.

George then got out of his vehicle and stabbed Mr McLean twice.

In sentencing, Justice David Lovell said George's offending was not on the lower end of the scale as he left the scene "not caring that he had stabbed someone".

During previous hearings, the Adelaide Magistrates Court was told the two men were driving in separate cars along Waterloo Corner Road on Saturday, November 25, 2017.

An altercation happened at the Salisbury Highway intersection about 10:40am.

Prosecutors alleged George stabbed Mr McLean before driving off.

Troy McLean was stabbed on the Salisbury Highway and later died in hospital. ( Supplied )

Mr McLean then tried to drive himself to the Lyell McEwin Hospital, in Elizabeth Vale, but crashed into a parked car on the way.

He was transferred to the Royal Adelaide Hospital in a serious condition, but died of his injuries three days later.

Defence lawyer Heath Barklay SC previously told the court that George was affected by a "cocktail of drugs" at the time of the altercation.

"He had been up for many days, was heavily affected by drugs and he accepts that he must have intended to cause grievous bodily harm," he said.

He said George's mental health had been declining in the months leading up to the offending and that he had been living the "life of a hermit" and was too anxious to leave his house.

The court heard photos of a bloodied knife taken on the day of the attack were found on George's mobile phone, but police had been unable to locate the knife.

The knife used by Benjamin Joshua George to fatally stab Troy McLean in 2017. ( SA Courts )

'My son is despised by many right now'

In a written statement read outside court this morning, George's mother Kylie McWilliams said she was deeply sorry for the struggles she knew the McLean family would continue to endure.

"I'd like to express how heartbroken I am for Troy's family and I know nothing can take away the immense, immeasurable pain," she said.

George's mother Kylie McWilliams (left) read out a statement following the sentence. ( ABC News: Claire Campbell )

"I know there are many people who see my son as a cold-hearted monster, but his actions that terrible day, that has forever changed two families, is not who he is or his story.

"My son Benjamin Joshua George is despised by many right now, but is also loved, adored and supported by the many that know him."

After reading the statement she said her family would still support George as much as they could.

"I know he's done something extremely terrible and unforgiveable by a lot of people but he's still my boy, I held him when he was born," she said.

"I didn't hold him thinking this is where we would be in 27 years."